Construction Methods in Carolingian Rome (8th-9th Cent.)

In the city of Rome, the period that runs from the pontificate of Hadrian I (771-795) to that of Leo IV (847-855) was marked by an exceptional volume of building activity: restoration works and new constructions that concerned not only religious buildings but also utilitarian architecture such as walls and aqueducts. This was due to the favourable political and economic conditions of the papacy that prevailed thanks to its liberation from Byzantine rule and the alliance with the Franks under Charlemagne. All the buildings of this period known today reveal the same construction characteristics, which were destined to disappear in the immediate years that followed: the materials used came from the stripping of ancient buildings; the foundations are tufa blocks, the curtain walls are brick, the mortars are made with violet-coloured pozzolana, the intonaco surfaces are extremely white, and the scaffold holes are small and circular. The attempt to imitate the techniques of classical antiquity is evident, as the extremely rare concrete vaulted constructions also testify. The norm in these structures, which differentiate them from the Roman ones, is in fact the irregularity of the laying: the brick courses are undulating; the surfaces are not flat but contain recesses and protrusions; and the joints are not uniformly finished on any one surface. If the uniformity of these constructions is the result of an uninterrupted activity and consistency of programmes permitted by the succession of popes all belonging to the Roman aristocracy, the technical characteristics are only partly justified by the use of non-homogeneous material as a result of their recovery or of hurried workmanship or even of a presumed loss of technical capacity, not apparent in other fields. Among the principal causes one must also consider the possible employment of unskilled labour: some works are known to have been carried out through public tender and also using forced labour, made possible by the political and economic structure of the Papal State.