It had been the custom for the king, and subsequently for the consuls, to make an estimate, at certain intervals of time, of the effective military strength of the state. This was originally a registration of all the patrician burgesses; but, after the Servian reforms, it became a numbering of all the citizens, for the purpose of discovering those liable to military service, the class in which they should be enrolled, and, in case of tribute being imposed, the liability of each household to the property-tax (_tributum_). For these purposes it was sufficient for the heads of families (_patres familiarum_) to be summoned and questioned. Their answers formed the record, in accordance with which military and financial burdens were imposed, and political influence in the _comitia centuriata_ was determined. The recognition of citizenship itself was dependent on this enrolment, for it is probable that from the earliest times membership of a tribe was the symbol of the possession of civic rights; while now the fact that the tribe was the basis of the _concilium plebis_ and the _comitia tributa_ gave a vote to every one enrolled in one of the _tribus_. The importance which the census had assumed was not compatible with the consular performance of its duties. The judicial and military functions of the annual magistrates interfered both with its regularity and its completeness, and the temporary suspension of the consulship offered a chance of vesting these duties in other magistrates. In the year 443 B.C. two new officials, called _censores_, were created,[446] who were to be elected by the _comitia_ of the centuries. The office was to be confined to the Patriciate, possibly because it was felt that the solemn ceremony of purification (_lustratio_) which closed the census could not adequately be performed by plebeian hands. No one as yet dreamed of the future greatness of the office; its beginnings were small,[447] and the tribunes offered no opposition to the law which established an office which was to become the greatest of political prizes.