Unfortunately the majority of surface cemeteries have been destroyed, and we know them more from literary or epigraphical sources than from surviving monuments. They were surrounded by an enclosure or marked out by boundary stones; they generally had graves dug in the ground formae, Reno Map Tourist Attractions often connected in a close network and deep enough to hold a dozen bodies on top of each other, separated by earthenware slabs, flat or sloping. More distinctive burials were those in terracotta, stone, marble, lead and, in some places, wooden sarcophagi. The decoration of marble sarcophagi was the beginning of early Christian sculpture. They were lined up along the enclosing walls, often under a roof sub teglata, or in shrines, or in the mausoleums that are the characteristic buildings of sub divo cemeteries. During the period of peace, they formed extensive complexes attached to the cemeterial basilicas of the martyrs. Special types of tombs in some regions are the vast fields of capuchin tombs as at Timgad, the stone chests once embellished with mosaics and inscriptions as at Tipasa, the semicylindrical masonry coffins cupae, cupellae, or the humble burials inside pieces of amphora as at Tarragona. III. Development and organization of cemeteries. One of the causes that most contributed to developing the Christian cemeteries and leading to profound changes in them was the cult of the martyrs buried during the persecutions. The search for places nearest to the venerated grave, as if to guarantee protection and salvation, caused the opening of new galleries and cubicles in underground cemeteries, and the accumulation of mausoleums and tombs in cemeterial basilicas sub divo i.e., in the open air. Such devotional tombs were called retrosanctos. For the less fortunate, more distant additions were made to the catacombs, also made necessary by the evergrowing numbers of the Christian population.