The Battle of Carrhae was fought in 53 BC between the Roman Republic and the Parthian Empire near the town of Carrhae.

It is commonly seen as one of the earliest and most important battles between the Roman and Parthian empires and one of the most crushing defeats in Roman history. Commander Parthian Surena crushed the Roman invasion force led by General Marcus Licinius Crassus. This was one of several battles that were to be fought between Rome and the Arsacid Dynasty. This was perhaps the greatest defeat suffered by the Romans in a long time.

How did it all begin?

Crassus, a member of the First Triumvirate and the wealthiest man in Rome, had been motivated by the prospect of military glory and riches and decided to invade Parthia without official consent from the Senate. The war in Parthia resulted from political arrangements intended to be mutually beneficial for Marcus Licinius Crassus, Pompeius Magnus, and Julius Caesar — the First Triumvirate.

Strength

Crassus arrived in Syria in late 55 BC and immediately set about using his immense wealth to raise an army. He assembled a force of seven legions (about 35,000 heavy infantry). In addition he had about 4,000 light infantry, and 4,000 cavalry, including the 1,000 Gallic cavalry Publius had brought with him (Plutarch. Life of Crassus, 20.1). Crassus also received aid from the Hellenic settlements in Syria and support of about 6,000 cavalry from Artavasdes, the Armenian king.

Invasion

After rejecting an offer of help from Artavasdes II King of Armenia to use its territory to invade the Parthian kingdom, Crassus marched his army straight through the desert of Mesopotamia. In response, the Parthian king Orodes II divided his army and took most of the troops to attack the Armenians and left the rest of his forces, about 9,000 horse archers and a thousand cataphracts under the command of General Surena. Orodes not foresee that forces of Surena (outnumbered at least 4 to 1) would be able to defeat Crassus.

Crassus received directions from the Arab chieftain Ariamnes, who had previously assisted Pompey in his eastern campaigns. Crassus trusted Ariamnes, but Ariamnes was in the pay of the Parthians. He urged Crassus to attack at once, giving false information that the Parthians were weak and disorganized. He then led Crassus's army into the most desolate part of the desert, far from any water.

Crassus then received a message from Artavasdes, claiming that the main Parthian Army was in Armenia and begging him for help. Crassus ignored the message and continued his advance into Mesopotamia. He encountered Surena's army near the town of Carrhae.

Battle

Crassus's army panicked after being informed of the presence of the Parthian army. His general Cassius recommended that the army be deployed in the traditional Roman fashion, with infantry forming the center and cavalry on the wings.

"And at first they purposed to charge upon the Romans with their long spears, and throw their front ranks into confusion; but when they saw the depth of their formation, where shield was locked with shield, and the firmness and composure of the men, they drew back, and while seeming to break their ranks and disperse, they surrounded the hollow square in which their enemy stood before he was aware of the maneuver." Plut. Crass. 24.3

Crassus' generals advised him to make camp, and attack the next morning in order to give his men a chance to rest. Publius, however, was eager to fight and managed to convince Crassus to confront the Parthians immediately.

Surena sent his horse archers to surround the Roman square. The horse archers then began to shower the legionaries with arrows. The Parthian's composite bows were powerful enough to pierce the legionary's armor and partially penetrate the legionary's shields. The Romans repeatedly advanced towards the Parthians to attempt to engage in close-quarters fighting, but the horse archers were always able to retreat safely, firing Parthian shots as they withdrew.

The legionaries then formed the Testudo Formation, in which they locked their shields together to present a nearly impenetrable front to missiles. However, this formation severely restricted their ability to fight in combat. The Parthian cataphracts exploited this weakness and repeatedly charged the Roman line, causing panic and inflicting heavy casualties.

The battle comes to an end

Surena used thousands of Camel Cavalry to resupply his horse archers. Crassus dispatched his son Publius with 1,300 Gallic cavalry to drive off the horse archers. The horse archers outflanked the Gauls and cut off their retreat. Publius and his men were slaughtered. Crassus, unaware of his son's fate but realizing Publius was in danger, ordered a general advance. He was confronted with the sight of his son's head on a spear (Plut. Crass. 26.4). Crassus, deeply shaken by his son's death, ordered a retreat to the nearby town of Carrhae, leaving behind thousands of wounded, who were captured by the Parthians.

The next day Surena sent a message to the Romans, offering to negotiate with Crassus. Surena proposed a truce, allowing the Roman army to return to Syria safely, in exchange for Rome giving up all territory east of the Euphrates.

The effects of the battle

After the humiliating defeat, Rome was terribly frightened by the possibility of an invasion of the eastern territories by the Parthians. The most significant impact of the defeat in the internal politics with the end of the first triumvirate that would put the other two triumvirs at war, would result in the end of the old Roman Republic and the birth of the Empire.