In order to provide a supply of competent officers, each eques was required to fill certain subordinate posts, called militiae equestres.
It may be remarked too in passing that in official Latin, not only in England but all over Europe, the word miles held its own against both eques and caballarius.
If competent, an eques could retain his horse and vote after the expiration of his ten years' service, and (till 129 B.C.) even after entry into the senate.
A sum of money (aes equestre) was given to each eques for the purchase of two horses (one for himself and one for his groom), and a further sum for their keep (aes hordearium); hence the name equites equo publico.
Extreme youth was no bar; the emperor Marcus Aurelius had been an eques at the age of six.