was usurped by the emperors, membership in a tribe remained an important part of Roman citizenship, so that the name of the tribe came to be incorporated into a citizen's full nomenclature. The number of tribes varied over time; tradition ascribed the institution of thirty tribes to Servius Tullius, the sixth King of Rome, but ten of these were destroyed at the beginning of the Republic. Several tribes were added between 387 and 241 BC, as large swaths of Italy came under Roman control, bringing the total number of tribes to thirty-five; except for a brief experiment at the end of the Social War in 88 BC, this number remained fixed. The nature of the tribes was mainly geographic, rather than ethnic; inhabitants of Rome were, in theory, assigned to one of the four "urban" tribes, while the territory beyond the city was allocated to the "rural" or "rustic" tribes. Geography was not the sole determining factor in one's tribus; at times efforts were made to assign freedmen to the four urban tribes, thus concentrating their votes and limiting their influence on the comitia tributa. Perhaps for similar reasons, when large numbers of provincials gained the franchise, certain rural tribes were preferred for their enrollment. Citizens did not normally change tribes when they moved from one region to another; but the censors had the power to punish a citizen by expelling him from one of the rural tribes and assigning him to one of the urban tribes. In later periods, most citizens were enrolled in tribes without respect to geography. Precisely when it became common to include the name of a citizen's tribus as part of his full nomenclature is uncertain. The name of the tribe normally follows the filiation and precedes any cognomina, suggesting that its addition preceded formal recognition of the cognomen — thus, no later than the second century BC. However, in both writing and inscriptions, the tribus is found with much less frequency than other parts of the name; so the custom of including it does not seem to have been deeply ingrained in Roman practice. As with the filiation, it was common to abbreviate the name of the tribe. For the names of the thirty-five tribes and their abbreviations, see Roman tribe. Women's names In the earliest period, the binomial nomenclature of praenomen and nomen that developed throughout Italy was shared by both men and