ANNA TARWACKA

Cardinal Stefan Wyszynski University in Warsaw

Rooted in Law. Roman Insights on the superficies solo cedit Principle

SUMMARY: 1. Introduction. – 2. Superficies solo cedit as a general principle in private law. – 3. Specificities of acquiring ownership of buildings erected on the seashore. – 4. The principle of superficies solo cedit in public law. – 5. The case of Pliny the Younger. – 6. Conclusions. – Abstract.

1. – Introduction

The principle of superficies solo cedit – that the owner of land is entitled to anything permanently attached to it – stands as a hallmark of Roman legal ingenuity. This rule provided a cohesive framework for addressing ownership and attachment, ensuring that land and its attachments were treated as a unified entity under the law. Unlike the norms of other ancient legal systems, Roman jurists applied this principle with remarkable consistency across property disputes, inheritance cases, and obligations.

This article explores the evolution, application, and exceptions to superficies solo cedit within Roman law. By examining its role in both private and public contexts, the discussion sheds light on the principle’s enduring influence and its nuanced operation within a complex legal system.

2. – Superficies solo cedit as a general principle in private law

The Romans distinguished various ways of acquiring property[1] deriving from natural reason (naturalis ratio) and the ius gentium, as well as from the ius civile[2]. In the second book of the Institutes, Gaius addressed this issue by describing, among other things, cases of the attachment of movable things to immovable property[3], among which he listed the erection of a building, the planting of a plant[4] and the sowing of grain on someone else’s land[5]. The jurist reported that in each of these three cases, there was an acquisition of ownership of the attached movables by the landowner[6]. This happened at the moment of permanent connection to the land. However, Gaius stressed the need for a settlement between the parties in cases where the owner claimed the land. The one who built, planted or sowed should be reimbursed for the expenses incurred, provided, however, that he was a bona fide possessor. Indeed, if the landowner sued with rei vindicatio and did not return the expenditures, the defendant could apply exceptio doli.

In the passage in question, Gaius also gave the basic rule governing this type of property acquisition: superficies solo cedit[7], which means only that what is permanently[8] attached to the land falls to the land[9], and thus becomes the property of the landowner. The same Gaius, in his commentary on the Provincial Edict, affirmed that under both the ius civile and the law of nature, ownership of structures erected on someone else’s land (in this case rented land) accrues to the one who owns the land[10]. This principle has been invoked by numerous jurists in various contexts. It is worth examining their views, in particular in relation to buildings erected on someone else’s land.

The aforementioned Gaius emphasised the relevance of the good faith premise in relation to the possibility of accounting for expenditure incurred in constructing on someone else’s land. This issue was considered in detail in the context of the erection of a building on land that the buyer had purchased from a seller who was not the owner, resulting in eviction. In his commentary on the edict, Ulpian considered the case described earlier by Julian[11], where someone bought land in good faith, but later found out that it was not owned by the vendor, and nevertheless erected a building on it. The question is whether the builder was definitely not entitled to exceptio. Ulpian acknowledged somewhat ironically, using a procedure akin to argumentum ad absurdum, that no, unless one were to say that the exceptio was due because of a damage that someone had himself caused[12]. The jurist added, however, that the purchaser could take away (ius tollendi) the structure he had erected as long as this would not expose the landowner to harm[13].

Celsus, on the other hand, considered the case of a person who unknowingly (imprudens) bought land from a seller who was not the owner, and then built something there or planted something[14], and then eviction happened[15]. Celsus wrote that a good judge (bonus iudex) should decide the settlement between the litigants according to the facts. If the owner wanted to build or plant anyway, he should return the expenditure to the extent that the land had increased in value. If, on the other hand, the owner was poor and returning the expenditure would result in the neglect of the lares and ancestral tombs, the builder/planter would only be entitled to the ius tollendi, with the proviso that the land should not be degraded and that nothing should be taken in bad faith if it was of no use but only damaged (e.g. frescoes scraped off the walls). In such a situation, the owner could also offer the equivalent of what the builder would take from the land. On the other hand, if the owner intended to sell the land anyway, he should reimburse the builder for the expenses incurred, as in the first case, and if not, the condemnatio would only be for the difference between the value of the land and the expenses incurred. Celsus' opinion is very long and detailed. The jurist mainly took into account the principles of equity. The buyer had acted in good faith. However, Celsus did not consider the application of the exceptio doli. Rather, his opinion seems to refer to a situation where the landowner was willing to pay compensation to the builder, and the exceptio only applied when the landowner refused to settle with a bona fide possessor who had built something on the land. The jurist considered that compensation should not always be in the form of restitution and made its nature dependent on the facts of the case. It is worth noting that the term bonus iudex (and also aequus iudex) appears in Seneca's treatise De ira. The philosopher wrote that such a judge should not decide differently in his own case and in the case of others, and that he should not hate but only condemn improper behaviour[16]. Celsus can therefore be seen to have invoked a certain paradigm, similar to the bonus vir construction often used by jurists.

Ulpian, discussing the case of a person who demolished someone else's house in order to erect baths there, held that he was liable for the destruction of another's property on the basis of actio damni iniuria dati[17]. He also added that in the case described, the principle of natural law was at work, according to which a building erected on someone else's land is acquired by the owner of the land. The defendant therefore lost twice: the baths he had built became the property of the landowner and, in addition, he had to pay a penalty for causing damage to someone else's property, i.e. to cover the losses caused by the demolition of the house.

Paulus, on the other hand, stated that if someone, when transferring ownership of real estate by traditio[18], reserved that he was only handing over the land, without the buildings, he would not have achieved anything, since they inherently belong to the land[19]. Such a ruling would have to be applied in any case of transfer of land, including mortis causa, as well as in the case of acquisition by usucaption[20]. However, this last point must have been debated, as can be seen from excerpts from Cicero's works. In the treatise Topica[21], the author raised doubts about the time needed to acquire a building: should it be compared to the time required for land, i.e. set at two years, or should it be related to other things and set at one year. On the other hand, in his speech Pro Caecina[22], Cicero stated that the XII Tables[23] provided for a two-year period for the usucaption[24] of land and this provision was also applied to buildings, indicating that this interpretation was well established. This is also what Gaius later wrote[25] and it is in accordance with the principle of superficies solo cedit: after all, it is difficult to consider that the usucaption of land should last longer than that of a building that shares its status.

According to Pomponius[26] in a situation where a wife would receive land from her husband as a donation and then build a tenement there, it would become the property of her husband. This seemingly paradoxical case should be explained on the basis of Roman matrimonial law, which prohibited donations between spouses. This prohibition constituted lex perfecta and therefore the donation made was invalid. Hence, it is further to be concluded that the land continued to be owned by the husband and, consequently, also the tenement built on it, in accordance with the principle of superficies solo cedit. In doing so, the jurist pointed out that, in the event that the husband brought a rei vindicatio, the wife could keep the tenement until the expenses were reimbursed (ius retentionis).

Javolenus, in his commentary on the work of Cassius, described a case where a testator bequeathed to someone in legacy a piece of land on which a building was later erected, after the will had already been made[27]. The jurist held that the building would also be the subject of the bequest, which is in accordance with the principle of superficies solo cedit. In this case, the type of legacy does not matter, although the use of the verb debebitur seems to indicate a legatum per damnationem. Pomponius, on the other hand, emphasised[28], that in the event of the burning of a tenement bequeathed in a legacy, the legatee had the right to vindicate the land.

Julian considered a complicated situation where the testator had bequeathed land to someone in the form of a legacy to the exclusion of a building[29]. The factual situation was thus that the subject of the legacy was made a large landed estate on which there was also a building, and the testator wanted the legatee to receive the land itself, but without the house. According to the jurist, such a bequest could be interpreted in two ways: either the exemption was to apply only to the building, or also to the land on which it stood (not the whole land, just the piece with the house). In the first case, the legatee could vindicate the whole land, including the building, but the heir would be entitled (thanks to the application of the exceptio doli) to the right to live in the villa (habitatio) and the servitudes allowing him to reach it (iter and actus). This opinion is based on the fact that the exclusion of the building itself is to be treated as ineffective in light of the principle of superficies solo cedit. In the second case, on the other hand, the legatee will be able to vindicate all the land except the villa, and the heir ipso iure will obtain a servitude of passage. Here, too, the jurist ruled according to the principle of the building belonging to the land, since the exclusion applied to both the villa and the land on which it stood. Finally, Julian also added that, if there was any doubt as to the intention of the testator, it should be assumed that he intended the exclusion to cover the building together with the land[30]. The jurist therefore attempted to introduce a presumption to assume that the testator used the term ‘building’ to refer to the entire structure, including the land. Such a presumption involves a supposition of knowledge of the rule of superficies solo cedit and makes it possible to protect the interests of the beneficiaries of the will, in the case of this particular case – the heir who was to receive the villa despite the establishment of a legacy.

The same Julian also reflected on another inheritance problem concerning superficies as a right on another's property, which in Roman law was a hereditary and transferable right consisting in the use of a building erected on another's land[31]. This right developed gradually due to the limited amount of land in the city. People who did not have the opportunity to obtain land ownership erected buildings on other people's plots of land. This involved the ownership of the building passing to the landowner, while the builder obtained the right to use the building he had erected. Julian held that if someone bequeathed the said right by legacy to the owner of the land[32], this had the effect of extinguishing the right. A building which was the subject of a right on another's land was the property of the landowner. Obtaining this right by legacy had the effect that ownership no longer suffered restrictions and the right to superficies itself was extinguished by merging with the right of ownership (confusio).

The link between the building and the land is also relevant in the case of other rights over another person's property. Paulus pointed out[33], that if a house is the object of the pledge, the land is also covered by it[34]. The same jurist also resolved a more complicated case[35], in which a house given as a pledge was destroyed by fire and then Lucius Titius bought the plot of land on which the burnt building stood and built a new house, casting doubt on the continued existence of the pledge. Paulus held that the pledge continued to exist and included the new building, which was covered by it by virtue of having been erected on the land covered by the pledge. However, he added that the bona fide possessor would only have to surrender the building to the creditors if he was reimbursed for the construction expenses incurred. The facts as described may be questionable. In the text the pledge was referred to by the term pignus, whereby the pledgee received the thing only in detentio. Here, however, it must rather have been a hypothec. In the event of non-payment of a debt by the debtor, the creditor could bring an in rem action against the purchaser of the land effective erga omnes. The limited right in rem encumbering the object of the contract of sale constituted a legal defect in the goods, so the purchaser could sue the seller with an actio empti, but in addition to this, the jurist held that he was entitled to a right of retention against the pledgee.

Javolenus argued[36], that in the case of a tenement being given in usufruct, this servitude also includes the right to use the land on which the erected tenement is located, as long as at least part of the tenement remains[37]. It must therefore be inferred that the complete demolition of the building would cause the usufruct to cease. Similarly, Paulus held[38], that the demolition of a house results in the termination of the servitude of overhangs (servitus stillicidii), even though the land is part of the building. This had to do with the purpose of establishing servitudes, which could not be exercised if there was no building. The usufruct of land recorded in the legacy was extinguished, according to Ulpian[39], when a building was erected on the land, which also seems to follow from the purpose of establishing ususfruct. If the servitude was intended to benefit from the land, it would be difficult to use it after the building had been erected. The deliberate action of the owner who would erect the building was considered to be malicious and gave a reason to sue.

The rule in question was also discussed in the context of interdictal protection with regard to the interdict uti possidetis, which applied in the case of a dispute over possession of real estate. From the wording of the praetor's order, it appears that, as a general rule, possession was maintained by the party to the dispute who was the just possessor (nec vi, nec clam, nec precario) of the land in dispute at the time the interdict was issued[40], but in the case of buildings standing on land, the problem could become more complicated. Ulpian described the case of the construction of a superstructure projecting over a neighbour's land and cited Cassius' opinion that in such a situation the interdict did not apply on the grounds that one party was in possession of the land and the other was in possession of the building including the superstructure, which belonged to the neighbouring property[41]. The jurist here did not dwell on the question of obtaining other means of protection, but it should be noticed that, where the land was owned, actio negatoria could be used.

Ulpian also considered, in the same context, the case of an attic over a house in someone's possession which someone else occupied, behaving as the owner[42]. The jurist cited Labeo’s opinion according to which interdictal protection was due to the possessor of the house and not to the occupier of the attic, because the building belongs to the land and not vice versa. This situation is simpler because it concerns one building erected on the land in question. The dispute is over individual rooms which, according to the principle of superficies solo cedit, belong to the land along with the entire structure.

One of the texts preserved in the Digests may testify to the existence of disagreements among jurists with regard to the principle in question. It concerns a passage in which Pomponius cited the different views of earlier jurists on the situation when someone erected a structure over someone else's wall[43]. Labeo and Sabinus considered such a structure to be the property of the builder, while Proculus, on the contrary, assumed that it belonged to the owner of the wall due to the fact that it was erected on his land. One might wonder why this difference of opinion. Proculus’ view, which was also unconditionally supported by Pomponius, is in accordance with the principle of superficies solo cedit. Why, then, did Labeo and Sabinus see it differently? It seems that the case should be applied to the Roman socio-legal reality. In the case of neighbouring properties, a builder might build a house against the wall of a neighbour. In such a situation, servitus oneris ferendi was established[44]. Perhaps in the case in question, the builder did not so much base his construction on an already existing wall, but additionally added something on top of it and the doubts about ownership concerned this very superstructure and not the entire structure. In the case of a servitude, the wall remained the property of the owner of the servient land, but the added house obviously did not. It can therefore be assumed that the jurists had different concepts due to the fact that the dispute did not concern the entire building, but only a piece of the wall. It is worth mentioning at this point that the servitude to rest the wall against the wall of the neighbour's building was the only one that required the servient party to behave actively, as it was he who had to carry out repairs[45]. Therefore, the question of ownership in the case in question could also have raised doubts for jurists: granting ownership of the over-built piece to the owner of the servient property could have resulted in the owner being burdened with additional repair costs.

From a legal point of view, it was also relevant when a building erected on someone else's land was later demolished. Gaius made the possibility for the person who erected the structure to recover the materials dependent on his state of mind[46]. If one built deliberately on someone else's land, then it can be assumed that he also accepted the loss of ownership of the materials[47], and was not entitled to rei vindicatio even after the building was demolished. A contrario, it can be assumed that a builder who was not aware that the land was someone else's could apply rei vindicatio when the house was demolished and the materials became separate things again. However, such situations were unlikely to arise because, as Gaius pointed out, the builder was entitled to claim reimbursement of his expenditure (cost of materials and labour). On the other hand – as Gaius conveyed[48] – when it was the owner of the land who erected a structure on it using someone else's materials, he acquired ownership of those materials, but once the building was demolished, they were subject to recovery from their original owner. Ownership of the materials therefore passed to the landowner in this case only for the duration of their incorporation into the building, as was already apparent from the XII Tables. However, when they became separate things again, they reverted to the original owner[49]. The latter's right did not expire completely, but only for the duration of the incorporation of the materials into the building. After the demolition of the building, he again obtained the protection to which he was entitled, whether on the basis of rei vindicatio or actio ad exhibendum.

The general rule of superficies solo cedit discussed above was not only known in juristic circles. A metaphorical reference to it can also be found in Seneca's letters[50]. The author, comparing philosophy and mathematics, considered that the latter, unlike the former, is not independent because it builds on certain accepted assumptions, i.e. on someone else's ground; philosophy, on the other hand, strives for truth by investigating good and evil, and draws nothing from other sciences.

It seems, therefore, that attaching a building to the ground was not a questionable issue in Roman law[51]. However, this was a typically Roman solution, different from the rules applied in other communities. Local customs in the eastern provinces, on the other hand, allowed for the separation of ownership of individual floors in buildings[52], as indicated by documents of legal practice[53], Liber Syro-Romanus[54] and a treatise by Julian of Askalon[55]. It was, however, one thing to allow the application of local law and another to recognise in Roman law derogations from the principle of superficies solo cedit. Justinian law clearly sought to apply this rule in an absolute manner[56].

Some scholars consider a passage from the Epitome Gai[57], an abridgment of Gaius’ Institutes as evidence of the existence of deviations[58] from the general principle of the connection between buildings and land in post-classical law. The author cited, albeit in a slightly modified form, the general principle that what is placed over something accrues to what is underneath (superposita inferioribus cedant), and went on to state that if someone builds a building on someone else's land, without permission, it becomes the property of the landowner. A contrario, it is argued that the landowner's consent caused the builder to acquire ownership[59]. At least two arguments can be made against this interpretation. Firstly, in the following passage, the author of the work wrote about the planting of trees, vines and other plants, as well as the sowing of crops, the ownership of which passed to the landowner regardless of his consent. Secondly, it should be noted which passage of the Institutes has been omitted here: the author of the Epitome only later in the text and in a more general context mentioned the necessity of settling the expenditure[60]. Meanwhile, in the case of a person who unknowingly built on someone else's land, exceptio doli and retention of the building was after all possible. The passage sine nostro permissu should therefore perhaps be regarded as a rather clumsy attempt at abbreviating from the original. On the other hand, the view that the consent of the landowner could be equivalent to the establishment of superficies[61] deserves recognition.

3. – Specificities of acquiring ownership of buildings erected on the seashore

The status of the sea and its shores was a complicated issue for the Romans[62]. Jurists emphasised their universal availability and the possibility of fishing, which was supposed to follow from the ius gentium[63]. It was not only the interest of private individuals who wanted to use the sea and its resources that was protected here, but also the public interest, since the economic development of the state made the sea a strategic element, both from the point of view of trade and for military reasons. It was possible to build on the seashore, for example, fishermen were allowed to erect a hut or shack[64]. However, the property regime was very particular in such a case.

In the writings of Neratius[65], a jurist from the first century AD, there is an interesting passage in which the author admittedly considered that seashores are public[66], but not as things owned by the people, but as those issued by nature and therefore not owned by anyone[67]. He likened the status of the shore to that of fish and wild animals, whose property is acquired when they are captured. According to Neratius, therefore, the acquisition of ownership of the seashore took place through occupatio. The person erecting a structure there took possession of the land and thus, by exercising control over it, became the owner both of the land itself and, in accordance with the principle of superficies solo cedit, of the structure erected on it.

Neratius' further statement[68] shows that the analogy with occupatio can also be extended to the moment of loss of ownership. In the case of wild animals, the escape and return of the animal to a state of natural freedom resulted in a return to its former status as a no-man's-thing (res nullius) and the possibility of appropriation by another person[69]. The situation was similar in the case of the seashore after the removal of a building: it reverted to its former status, i.e. according to Neratius, it became a public thing again and another person could build on it.

By contrast, both the sea and the seashore were placed by the later jurist Marcianus in the category of things common to all – res omnium communes[70]. This assignment of them was supposed to result from natural law. Accordingly, everyone had the right to fish by the sea, and preventing access to the shore could result in liability for iniuria on the basis of an actio iniuriarum aestimatoria[71].

According to Marcianus[72] the builder became the owner of the land on which he had erected the structure, but only as long as it stood. The collapse of the building meant that the section of seashore in question once again became a common thing for all and someone else could erect another structure on it. The jurist very artfully likened this principle to the institution of the right of return – ius postliminii, which allowed those returning from captivity at the hands of enemies to regain their former status.

The contradiction between the solution described by Marcianus and the principle of superficies solo cedit is striking. Here, it was the fisherman who, by erecting a hut, acquired ownership, and not only of the structure itself, but also of the land on which it was erected. Admittedly, the solution proposed by Neratius was complicated, but at least it allowed the correct order to be followed: first the appropriation of the land, then the acquisition of ownership of the building, which constitutes the superficies.

There seems to have been a difference of opinion between the jurists on the question of placing seashores in a particular category of thing. Neratius apparently had trouble with categorisation. Although he recognised them as public things to some extent according to the law of nature, his solution to the problem was based on assimilating them to res nullius[73]. Marcianus, on the other hand, categorised them as things common to all (res omnium communes).

Both opinions were based on the same ratio: the desire to protect[74] the person who was erecting the structure on the seashore in the event of a dispute, whether with another builder, a fisherman or a nearby property owner. Structures erected on the seashore could be destroyed in the event of a storm or strong winds. However, if it was human action that led to their demolition, then the builder could bring an action, probably an actio damni iniuria dati, even if he had already lost his property in accordance with the rules described.

The views of Pomponius[75] also seem interesting in the context of these considerations. The jurist considered two cases: building on poles placed in the sea and constructing an island. In both cases, he conceded ownership of the structure to the builder, invoking the principle that a thing belonging to no one accrues to the first appropriator – res nullius cedit primo occupanti. Neither the structure on stilts nor the island existed beforehand and therefore had no owner, and this seems to determine the solution used. Pomponius did not at all link the solution of the case to the question of ownership of the ground. This is probably because the jurist was looking at the cases in question as situations where someone builds ‘on the sea’[76], not on the ground. The structures would therefore be things in their own right and not superficies.

In another text[77] Pomponius stated that although what we build on the public shore or at sea is ours, the praetor's permission is needed; otherwise someone may prevent us from building. This text shows that Pomponius had no doubt that a building erected on the public shore or at sea becomes the property of the builder. He too, like Neratius, used the adjective publicus. Pomponius further added that the builder needed a decree, i.e. a decision expressing the praetor's consent, otherwise he could be stopped, presumably by virtue of the interdict Ne quid in loco publico fiat[78]. The need to obtain a decree, however, did not arise in the case of fishermen[79], who erected temporary structures, but when someone wanted to build a more permanent structure that might disturb someone.

Ulpian, in turn, wrote in his commentary on the edict[80], that what someone builds on the sea or its shores, even if he does not build on his own, becomes his by virtue of the ius gentium. The principle of superficies solo cedit was derived by Roman jurists from natural law and naturalis ratio, which was already expressed as ius gentium in later texts. The status of the sea and its shores was also regulated by the ius gentium, with the adoption of the principle of its belonging to the land being problematic if a building was erected there. Ulpian's opinion confirms the different status of the sea and its shores and indicates a certain evolution of views. While Neratius tried to clarify the question of the acquisition of ownership of structures by applying an analogy with occupatio, later jurists passed over the problem by taking into account the different legal regime of these places.

The status of the sea and its shores was a major issue. Jurists agreed that the erection of a structure on the shore resulted in the acquisition of ownership of the land, which was intended to protect the builder, with the understanding that the construction itself (with the exception of fishermen's huts) had to be built with permission, otherwise it could be stopped by interdict[81]. It seems that the attempt to include the seashore among the things subject to occupation may have been aimed at aligning the decision to grant ownership of the structure to the one who erected it with the principle of superficies solo cedit. The protection of the public interest, on the other hand, was expressed firstly in the fact that the builder had to have the praetor's consent (except for fishermen), since otherwise he could be stopped by interdict, and also in the fact that the demolition of the structure resulted in the loss of ownership of the land.

4. – The principle of superficies solo cedit in public law

In Rome of the Republican period, the custody of public places was exercised by censors[82]. Their tasks primarily included the ability to demarcate public and private land, as indicated by inscriptions commemorating the setting of boundary stones[83]. In addition, the censors ensured that private persons did not occupy public land and buildings[84]. If something was built on public land, the censors had the right to order a demolition (demolitio), giving the builder a specific deadline to do so, while they could also seize some of his objects as security (pignoris capio).

However, the competence of the censors to erect public buildings such as aqueducts or roads seems most relevant to the considerations at hand. These were huge construction projects, for the realisation of which the censors entered into public contracts with private entities, usually publishing companies. These contracts were called locationes censoriae. However, a key problem arose regarding the ownership of the land through which the road or aqueduct would be routed. The land had to be owned by the state[85], and with such large investments this could be problematic.

Researchers here mainly argue about whether the censors had the right to forcibly expropriate landowners in order to obtain the land needed for construction. In particular, the term ius publicandi used in the sources, which can be understood as “the right to carry out expropriation”, is debatable[86]. However, such an interpretation does not seem to be supported by the surviving sources[87].

First of all, the source texts indicate that the censors bought the land on which they wanted to erect buildings, for example the Basilica Porcia, for the construction of which Cato, as censor, bought the shops (along with the land)[88]. Thus, there is no expropriation, there is publica emptio.

As the case of Marcus Crassus, who refused to allow an aqueduct through his land in 179 BC, indicates, the censors could not force permission to run an aqueduct through private land[89]. The land acquisition procedure involved acquiring such a piece of land as was needed. In the case of roads and aquaeducts, these were strips of land corresponding to the width of the structure with some allowance. Frontinus noted[90], that, if the owner was not willing to sell a piece of land, then the whole was bought from him and then, when the work was completed, the surplus was resold, the buyer from the state being, it seems, not the previous owner, but a willing purchaser who wanted to exercise his ownership of the land located either by the road or by the aqueduct. In the latter case, he could usually obtain the right to draw water quite easily.

It seems that the routing of the aqueduct must have been preceded by a thorough reconnaissance of the land through which it was to run and preliminary discussions with the people who occupied it. The seriousness of the censor's office played no small part in the persuasion. Even without any coercive measures, the censors were probably able to persuade the occupants of the land to sell off the part of it through which the aqueduct was to run. An additional incentive was probably the promise of a water concession. The case of Crassus described by Livy must have been exceptional. His refusal probably came after the route of the aqueduct had already been mapped out and the censors were forced to stop the already advanced work.

It can therefore be thought that the conversion of private land into public land in order to erect a structure on it did not involve the use of coercion. First, the censors acquired the land (buildings could stand on it, which were then also subject to purchase, and were then demolished in order to erect a new structure) by entering into a paid contract – publica emptio. Only then did the actual publicatio take place, i.e. the granting of the status of public land to the land. The competence to perform this action by an official is referred to in the sources as ius publicandi. However, it does not seem to imply expropriation, but only the possibility of deciding that the land is public.

The problem of combining movable and immovable property in the context of public law was referred to by the jurist Labeo in his work Pithana, describing the rules concerning the acquisition of ownership of an island created on a river[91]. The jurist stated that what is created in a public place or built there becomes public; similarly, an island created on a public river should be public. There is a debate in the literature on this text, because from the earlier passage D. 41.1.65.2 implies that an island created on a river becomes the property of the one closer to whose land it is located. One has to agree with the view of Agnieszka Kacprzak[92], according to whom Labeo tried to introduce here a solution contrary to the one used so far, arguing that his view is in accordance with the generally accepted principle of superficies solo cedit. In my view, however, there is no reason to believe that superficies solo cedit was, until Labeo's time, a purely private law principle. In that case, the jurist would not have invoked it as a matter of course. Labeo merely wished to draw attention to the fact that in the case of an island formed on a river, this principle did not apply, which was an undesirable exception that had to be eliminated. Hence the phrase publica esse debet. The problem of the island is, however, a separate issue, as there is no attachment of movable to immovable property in its formation. It should be noted, however, that Labeo in his text mentioned not only the case of an island, but also of a building erected on public land which, according to the jurist, becomes public. The inaedificatio was therefore, it seems, a case of undisputed connection to public land, and Labeo reasoned analogously, likening the situation of the creation of an island to this case. This confirms the observation that the rule of superficies solo cedit itself was also applied in public law, whereas the jurist sought to extend its application to the different case of accession, recognising that the island, as it were, ‘inserts itself’ into the river, just as a building does into the land.

5. – The case of Pliny the Younger

Very interesting, in the context of the principle of superficies solo cedit, is the issue concerning the construction of a bathhouse in the city of Prusa in Bithynia, raised in the correspondence of Pliny the Younger with Emperor Trajan.

Pliny described in a letter to the emperor the issue of the complicated status of the land on which he wanted to erect the building of the new baths for the inhabitants of the city[93]. This was the site where a beautiful house had once stood, but which had fallen into ruin. This house was bequeathed in the form of a legacy by Claudius Polyaenus to the Emperor Claudius. The testator ordered that a temple be set up in the peristyle, while the rest of the house was to be rented out. The rental income was enjoyed by the local community for some time. Then, due to neglect, the house collapsed and eventually little was left there other than the land itself. Pliny suggested to the emperor that he should either donate the property to the civitas or sell it back to it. He added that he planned to erect baths on the land, while where the buildings stood he would build a rotunda and colonnades and dedicate the site to Trajan.

It is clear from the letter that Trajan, as emperor, became the owner of the property that his predecessor Claudius had received in the form of a legacy, and Pliny decided to use the location for the construction of the thermae. He wanted to bring about the transfer of ownership of the land to the local civitas, whether in a gratuitous or a pecuniary way, so that it would also include the thermae.

In response[94] Trajan gave permission for the construction of the baths. He pointed out, however, that if there was a temple in the peristyle of the destroyed house in honour of Claudius, the land underneath it became a thing in the power of the deities (res sacra). This caveat is very important, as it shows that the consecration of the building also resulted in a change in the status of the land. However, it must have been an act of consecratio of a public nature and not merely a private one. Then, even after the destruction of the building, the land still belonged to the res divini iuris. This is, moreover, in line with the statements of the jurists[95]. The question therefore arises whether in this case there is a violation of the principle of superficies solo cedit, since it was the land that, as it were, followed the building. While it is not possible to resolve this question unequivocally, it seems rather that the connection between the building and the land was taken for granted, and therefore the act of dedication probably naturally included the whole: both the land and the building[96].

6. – Conclusions

The rule of superficies solo cedit, which granted the owner of land entitlement to whatever was permanently attached to it, was a distinctly Roman solution, differing from the norms of other ancient legal systems. Roman jurists consistently applied this principle across a variety of cases, including those related to property law, inheritance, and obligations. However, deviations from the rule were possible in the provinces, where local laws sometimes allowed separate ownership of floors within a building.

An unusual exception to this principle applied to structures erected on the seashore. Jurists typically assumed that the builder acquired ownership of both the structure and the land on which it was built. Some sought to reconcile this with the principle of superficies solo cedit by arguing that the land was appropriated first, after which the structure became its attachment. Others, however, rejected this reasoning, treating the seashore as a unique category of land with its own legal status.

In the context of public law, the activities of the Roman censors, who oversaw construction projects, were closely tied to the application of this principle. Construction projects undertaken by the censors were often leased out to private entities. Importantly, public buildings were required to stand on public land. To facilitate this, the censors were responsible for acquiring necessary land, but there is no evidence to suggest they had the authority to expropriate private owners compulsorily. Instead, land was purchased through a process called publica emptio and then converted into public property (publicatio). According to the principle of superficies solo cedit, anything built on public land automatically became public property.

A further dimension of this principle involves the dedication of buildings. Roman sources indicate that even after the demolition of a consecrated building, the land it occupied retained its sacred status (res sacra). This suggests that the act of consecration applied to both the building and the land. As a result, any structure subsequently erected on such land would also inherit the status of a consecrated object.

Abstract

The rule of superficies solo cedit, which stated that the owner of land acquired ownership of anything permanently attached to it, was a distinctly Roman solution, differing from the norms of other ancient legal systems. The writings of Roman jurists demonstrate that this principle was consistently applied in various contexts, encompassing not only property law but also inheritance, obligations, and aspects of public law.

Keywords: Roman law, superficies solo cedit, accessio, ius gentium, censors.