As the demands upon the services of the cavalry increased, it was decided to supplement the regulars by the enrolment of wealthy citizens who kept horses of their own. The origin of these _equites equo privato_ dates back, according to Livy (v. 7), to the siege of Veii, when a number of young men came forward and offered their services. According to Mommsen, although the institution was not intended to be permanent, in later times vacancies in the ranks were filled in this manner, with the result that service in the cavalry, with either a public or a private horse, became obligatory upon all Roman citizens possessed of a certain income. These _equites equo privato_ had no vote in the centuries, received pay in place of the _aes equestre_, and did not form a distinct corps. Thus, at a comparatively early period, three classes of equites may be distinguished: (a) The patrician equites _equo publico_ of the _sex suffragia_; (b) the plebeian equites in the twelve remaining centuries; (c) the equites _equo privato_, both patrician and plebeian. The equites were originally chosen by the curiae, then in succession by the kings, the consuls, and (after 443 B.C.) by the censors, by whom they were reviewed every five years in the Forum. Each eques, as his name was called out, passed before the censors, leading his horse. Those whose physique and character were satisfactory, and who had taken care of their horses and equipments, were bidden to lead their horse on (_traducere equum_), those who failed to pass the scrutiny were ordered to sell it, in token of their expulsion from the corps. This inspection (_recognitio_) must not be confounded with the full-dress procession (_transvectio_) on the 15th of July from the temple of Mars or Honos to the Capitol, instituted in 304 B.C. by the censor Q. Fabius Maximus Rullianus to commemorate the miraculous intervention of Castor and Pollux at the battle of Lake Regillus. Both inspection and procession were discontinued before the end of the republic, but revived and in a manner combined by Augustus. In theory, the twelve plebeian centuries were open to all freeborn youths of the age of seventeen, although in practice preference was given to the members of the older families. Other requirements were sound health, high moral character and an honourable calling. At the beginning of the republican period, senators were included in the equestrian centuries. The only definite information as to the amount of fortune necessary refers to later republican and early imperial times, when it is known to have been 400,000 sesterces (about L3500 to L4000). The insignia of the equites were, at first, distinctly military--such as the purple-edged, short military cloak (_trabea_) and decorations for service in the field.