The hill was constructed using mostly the fragments of large globular vessels from Baetica (the Guadalquivir region of modern Spain), of a type now known as Dressel 20. It also included smaller numbers of two types of amphorae from Tripolitania (Libya) and Byzacena (Tunisia). All three types of vessel were used to transport olive oil. However, it is not clear why Monte Testaccio was built using only olive oil vessels. The oil itself was probably decanted into bulk containers when the amphorae were unloaded at the port, in much the same way as other staples such as grain. There is no equivalent mound of broken grain or wine amphorae and the overwhelming majority of the amphorae found at Monte Testaccio are of one single type, which raises the question of why the Romans found it necessary to dispose of the amphorae in this way.