When the army on the march is near the place of encampment, one of the tribunes and those centurions who are specially charged with this duty go out in advance,
and after surveying the whole ground on which the camp is to be formed, first of all determine from the considerations I mentioned above where the consul's tent should be placed and on which front of the space round this tent the legions should encamp.
When they have decided on this, they measure out first the area of the praetorium, next the straight line along which the tents of the tribunes are erected and next the line parallel to this, starting from which the troops form their encampment.
In the same way they draw lines on the other side of the praetorium, the arrangement of which I described in detail and at some length.
All this is done in a very short time, as the marking out is a quite easy matter, all the distances being fixed and familiar;
and the now plant flags, one on the spot intended for the consul's tent, another on that side oit they have chosen for the camp, a third in the middle of the line on which the tribune's tents will stand, and a fourth on the other parallel line along which the legions will encamp.
These latter flags are crimson, but the consul's is white. On the ground on the other side of the praetorium they plant either simple spears or flags of other colours.
After this they go on to lay out the streets and plant spears in each street.
Consequently it is obvious that when the legions march up and get a good view of the site for the camp, all the parts of it are known at once to everyone, as they have only to reckon from the position of the consul's flag.
So that, as everyone knows exactly in which street and in what part of the street his tent will be, since all invariably occupy the same place in the camp, the encamping somewhat resembles the return of an army to its native city.
For then they break up at the gate and everyone goes straight on from there and reaches his own house without fail, as he knows both the quarter and the exact spot where his residence is situated.
It is very much the same thing in a Roman camp.
Walbank Commentary