on the backs of donkeys or mules and then broken up on the spot, with the sherds laid out in a stable pattern. Lime appears to have been sprinkled over the broken pots to neutralise the smell of rancid oil. As the oldest parts of Monte Testaccio are at the bottom of the mound, it is difficult to say with any certainty when it was first created. Deposits found by excavators have been dated to a period between approximately AD 140 to 250, but it is possible that dumping could have begun on the site as early as the 1st century BC. The mound has a roughly triangular shape comprising two distinct platforms, the eastern side being the oldest. At least four distinct series of terraces were built in a stepped arrangement. Layers of small sherds were laid down in some places, possibly to serve as paths for those carrying out the waste disposal operations. Re-use and disposal of amphorae 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. One possibility is that the Dressel 20 amphora, the principal type found at Monte Testaccio, may have been unusually difficult to recycle. Many types of amphora could be re-used to carry the same type of product or modified to serve a different purpose—for instance, as drain pipes or flower pots. Fragmentary amphorae could be pounded into chips to use in opus signinum, a type of concrete widely used as a building material, or could simply be used as landfill. The Dressel 20 amphora, however, broke into large curved fragments that could not readily be reduced to