A censor was a political officer of the Roman Republic. Two censors were usually elected by the Centuriate assembly every five years to serve an 18 month term. This office did not follow the usual Roman pattern of annual, one year terms, though it did follow the principle of collegiality by having two censors who served together. This office did not possess imperium and, due to this, censors were not escorted by lictors. If one of the censors died, the other was compelled to resign his post.
The office of censor was first created in 443 BC and, like most, was only open to patricians. The progressive influence of plebeians in the Roman society permitted the first non-patrician to be elected in 351 BC. During the dictatorship of Lucius Cornelius Sulla the office was abolished, but, reinstored in 70 BC.
The censors took a regular census of the Roman people and then of apportioning the citizens in voting classes on the basis of income and 'tribe' affiliation. Tribes in the Roman state were not ethnic but assigned by the censors - only the descendants of ancient citizen families considered themselves related to their tribe by blood. The censors enrolled new citizens in tribes and voting classes as well - slaves who had been freed since the last census automatically entered citizenship.
The censors were also in charge of the membership roll of the Senate, adding new senators every five years who had been elected to the requisite offices. After the Sullan reforms of 81 BC new senators were enrolled automatically, much reducing the influence of the censors over membership in the Senate. Censors were also responsible for construction of public buildings.