The Battle of Adrianople. 378 AD.

Arriving Gothic cavalry poured in from behind at this unfortunate timing and the Roman order of battle on their right flank crumbled. The Romans retreated to the base of the hill where the Goths were assembled and there they were surrounded and all killed. Other portions of the Roman line held for a time and made headway. But 4 PM, the rest of the Gothic cavalry poured in and routed the Romans. As many as 25,000 Romans may have been killed. Valens, himself was abandoned by his guards and died on the battlefield.