Roman line relief

[LonginusXXI]

Was there ever some sort of rank switching during battles between sections or centuries that the Romans used? Like a passage of lines?

[Robert Vermaat]

Was there ever some sort of rank switching during battles between sections or centuries that the Romans used? Like a passage of lines?

I can only answer that for the later Roman period in which it was extremely unlikely, given that the army took care to have the front rankers armoured if there wasn't enough for all to go around.
There's also a theory that the so-called 'antesignani' were soldiers who fought in the front ranks, protecting the officers and standard bearers who also led from the front, both of which would also make line relief difficult.

But I'm hardly an expert in such matters.

[Nathan Ross]

You might find this lengthy thread interesting:

Infantry Relief System

The general consensus seems to be that the Romans during some periods probably did have a way of relieving or replacing troops in the front lines - Dionysius (8.65) describes a republican commander ordering that "the troops which were still fresh and were being reserved for this very purpose should come up to reinforce the parts of the line that were in distress and that the men who were wounded and exhausted should retire to the rear." How common this was, and how it actually worked in practice, though, is unknown!