The division and appointment of the tribunes having thus been so made that each legion has the same number of officers,
those of each legion take their seats apart, and they draw lots for the tribes, and summon them singly in the order of the lottery.
From each tribe they first of all select four lads of more or less the same age and physique.
When these are brought forward the officers of the first legion have first choice, those of the second choice, those of the third third, and those of the fourth last.
Another batch of four is now brought forward, and this time the officers of the second legion have first choice and so on, those of the first choosing last.
A third batch having been brought forward the tribunes of the third legion choose first, and those of the second last.
By thus continuing to give each legion first choice in turn, each gets men of the same standard.
When they have chosen the number determined on — that is when the strength of each legion is brought up to four thousand two hundred, or in times of exceptional danger to five thousand —
the old system was to choose the cavalry after the four thousand two hundred infantry, but they now choose them first, the censor selecting them according to their wealth; and three hundred are assigned to each legion.
Walbank Commentary