Monte Testaccio was not simply a haphazard waste dump; it was a highly organised and carefully engineered creation, presumably managed by a state administrative authority. Excavations carried out in 1991 showed that the mound had been raised as a series of level terraces with retaining walls made of nearly intact amphorae filled with shards to anchor them in place. Empty amphorae were probably carried up the mound intact on the backs of donkeys or mules and then broken up on the spot, with the shards laid out in a stable pattern. Lime appears to have been sprinkled over the broken pots to neutralise the smell of rancid oil.