I'm not sure about the Romans, but certainly in Hellenic warfare it was common for the dead to be buried or returned home. Truces for burials were not uncommon, and I recall (though dimly) one battle in which the Spartans were defeated (possibly by Thebes?) at which the victors insisted the Spartans bury their allies first, to make the point over how many Spartans lay dead on the field. But of course this was in the more ritualised battles of hoplite warfare.