small shards. It is likely that the difficulty of reusing or repurposing the Dressel 20s meant that it was more economical to discard them. Another reason for not re-cycling olive oil amphorae into concrete of the opus signinum type may have been that the fragments were too fatty due to residual oil. Also, oil happens to react chemically with lime (a major component of concrete) and the product of this chemical reaction is soap; the resulting concrete would have had unsatisfactory quality. Wheat amphorae and wine amphorae on the other hand were certainly "clean" enough to be recycled into concrete. Tituli picti Monte Testaccio has provided archaeologists with a rare insight into the ancient Roman economy. The amphorae deposited in the mound were often labelled with tituli picti, painted or stamped inscriptions which record information such as the weight of the oil contained in the vessel, the names of the people who weighed and documented the oil and the name of the district where the oil was originally bottled. This has allowed archaeologists to determine that the oil in the vessels was imported under state authority and was designated for the annona urbis (distribution to the people of Rome) or the annona militaris (distribution to the army). Indeed, some of the inscriptions found on mid-2nd century vessels at Monte Testaccio specifically record that the oil they once contained was delivered to the praefectus annonae, the official in charge of the state-run food distribution service. It is possible that Monte Testaccio was also managed by the praefectus annonae. The tituli picti on the Monte Testaccio amphorae tend to follow a standard pattern and indicate a rigorous system of inspection to control trade and deter fraud. An amphora was first weighed while empty, and its weight was marked on the outside of the vessel. The name of the export merchant was then noted, followed by a line giving the weight of the oil contained in the amphora (subtracting the previously determined weight of the vessel itself). Those responsible for carrying out and monitoring the weighing then signed their names on the amphora and the location of the farm from which the oil originated was also noted. The maker of the amphora was often identified by a stamp on the vessel's handle. The inscriptions also provide evidence of the structure of the oil export business. Apart from single names, many inscriptions list combinations