How did soldiers in big battles with multiple tribes/nations identified friend or foe 500+ years ago?

by VirtualMoneyLover

For example in the Battle of the Catalaunian Plains they had the Romans, Visigoths, Burgundians, Franks, Saxons,etc. fighting the Hunnic Empire with Amali Goths, Sciriis, Thuringians, Heruli,etc.

More than a dozen different fractions. 451 AD, so uniforms are not a thing. The battle lasted 2 days, so when 2 groups of soldiers encountered each other in the fog of war, how did they know if it was friend or enemy?

dutch_penguin

A similar question has been asked a few times in the past. The answers collected here by u/Searocksandtrees. Also here by u/warlitter.