Proportions in early christian and early medieval Roman church structures

A large number of early Christian and medieval Churches remain in Rome, generally modified at various time periods. These churches, built of load bearing masonry in various sizes, represent the most successful typological choice adopted for the Christian liturgy. These buildings are distinguished by somewhat improvised construction and by the use of spolia, that is, elements removed from ancient Roman structures. Although there is no evidence of established rules for structural design of the period, the builders' empirical approach suggests that they intentionally used geometrical proportions as a guide to adopt structural decisions. In this study, we perform a comparative analysis of twenty-three Roman churches dating from about 300-1200 CE, considering several important structural attributes: the proportionality of the colonnade dividing the nave from the aisles, the intercolumniation ratio (the ratio of the clear column spacing to its diameter), and the type of the structure above (arcades, architraves, and relieving arches). The results show that arcades were the most common structure, with an average intercolumniation ratio of approximately 4, architraves were used for smaller intercolumniation ratios averaging 2.6, and relieving arches, often used as an intermediate solution, had intercolumniation ratios close to 3[1]. The structural choices of the intercolumniation are connected to the masonry system of the churches: they condition the way to build arches and to organize the upper level of the wall. In this sense, the organization of the system of isolated supports represents a crucial element of the masonry construction of the early Christian churches in Rome.