Middle republican triplex acies: a problem of space

[L C Cinna]

hmm my opinion always was that the maniples of the hastati and principes form the checkerboard formation. the centuries of each maniple behind each other, each century 8 to 10 ranks deep, so each maniple 16 to 20 ranks. when closing in on the enemy the 2nd century moves forward to fill the gap and make a closed battleline.
if the centuries stay 8 to 10 deep we'll get a closed line of hastati and a 2nd closed line of principes each 8 to 10 deep, so the triarii should in the end still be able to cover the rear in a line at least 4 to 5 ranks deep.

i don't think they kept the gaps and used to fill them with units from the 2nd line. then it just wouldn't make sense to have the 2 lines equipped differently.the change of worn out hastati centuries with fresh principes centuries would take place one by one during the breaks which occur in the battle. i really don't think the gaps were kept during the actual engagement. if you do it like i described above you can still have a 3rd line consisting of triarii which covers the same space as the units in the first 2 lines and they still have enough depht to form a strong defensive line if needed.