They now measure a hundred feet from the front of all these tents, and starting from the line drawn at this distance parallel to the tents of the tribunes they begin to encamp the legions, managing matters as follows.
Bisecting the above line, they start from this spot and along a line drawn at right angles to the first, they encamp the cavalry of each legion facing each other and separated by a distance of fifty feet, the last-mentioned line being exactly half-way between them.
The manner of encamping the cavalry and the infantry is very similar, the whole space occupied by the maniples and squadrons being a square.
This square faces one of the streets or viae and is of a fixed length of one hundred feet, and they usually try to make the depth the same except in the case of the allies.
When they employ the larger legions they add proportionately to the length and depth.
Walbank Commentary