Bulla Regia - Vaulting technique

The villas of Bulla Regia show an unusual method of constructing vaults which is found on many other Roman sites in Tunisia. It seems to have evolved in the second century and to have been used until the Arab conquest. A number of terracotta tubes were fitted into one another to form a dome shape and the joints were filled in; a number of such arches were set up next to one another to form a vault, and the under surface was then faced with plaster.