How long did Roman era battles last?

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The lines would simply pull apart and a lull would happen. For some time the troops would rest, drink some water, rotate the troops (or perhaps even whole lines) and pass up throwing weapons (pila comes to mind here). Then one side would initiate the combat again

That sounds rather unlikely to me Kraxis. I've never heard of an ancient battle where this happened. Conceivably where the defending side was considerably outnumbered but in a strong position, you might have waves of attacks, and pauses in between as the attackers reorganized for the next assault. But that's not quite the same as the mutual pause for rest and refreshment that you are suggesting.

Any examples you can cite?