The original titular churches of Rome were those which had been private residences and which were donated to be converted to places of Christian worship. Above an originally 1st century AD villa and its later adjoining warehouse and Mithraeum, a large basilica church had been erected by 350, subsuming the earlier structures beneath it as a crypt. The basilica was the first church of San Clemente al Laterano. Similarly, at Santi Giovanni e Paolo al Celio, an entire ancient city block – a 2nd-century "insula" on the Caelian Hill – was buried beneath a 4th-century basilica. The site was already venerated as the "martyrium" of three early Christian burials beforehand, and part of the "insula" had been decorated in the style favoured by Christian communities frequenting the early Catacombs of Rome.