During the second century, North Africa was one of the Roman empire's most important producers of food, supplying perhaps two-thirds of the grain consumed in Rome. In addition, North African olive oil was exported all over the Western Mediterranean. The Roman imperial government took a continuing interest in North Africa's importance as an agricultural center and so maintained control over a large proportion of North African farmland. One of the most important centers for imperial land was the fertile Bagradas valley in northern Tunisia. There, a regulation called the lex Manciana served as a basic lease arrangement for tenants cultivating land on imperial estates. Since the lex Manciana is attested only on North Africa, it seems to have been a regulation designed specifically for the conditions of that region and so represents part of the imperial government's long-term program of exploiting North African farmland.