What happened
In 53 BC, near Carrhae — modern Harran in southeastern Turkey — a Parthian army destroyed the invading Roman force of Marcus Licinius Crassus. The Parthian commander Surena, with perhaps 10,000 horsemen against some 40,000 or more Romans, used relays of horse archers resupplied by camel trains, and the famous feigned-retreat backward shot, to shoot the legions apart. Armored cataphracts broke every attempt to close, and Crassus’s son Publius died leading a doomed sortie. Crassus himself was killed during a parley; the tale that molten gold was poured into his mouth is a late and unverifiable legend. Some 20,000 Romans are said to have died and 10,000 to have been captured, and several legionary standards — the eagles — were lost.
Background
Crassus, the richest man in Rome and the third member of the First Triumvirate alongside Caesar and Pompey, invaded Parthia in search of military glory. As the ancient sources themselves complained, the campaign lacked a defensive pretext even in Roman eyes.
Consequences
The defeat fixed the Euphrates as the Roman–Parthian frontier for generations. It also helped unravel the Triumvirate; the civil war between Caesar and Pompey followed. The lost eagles were returned by diplomacy under Augustus in 20 BC and celebrated as a Roman propaganda coup.