Roman Battle Formation

[antisocialmunky]

I believe this concept originates with Tacitus (less than reliable on military matters, he says auxilleries used longer swords for ex.).

However, Tacitus records a rolling advance, which makes some sense, as the ranks move through each other the first two rotate to reduce fatigue and so that the enemy is constantly presented with an attacker.

In retreat it would work in reverse, so that the enemy was always presented with a static, solid, front.

This is how I've always imagined it working - a sort of leap frogging advance. Do you have the exact source so we can have more debate fodder?