Crassus began with 7 legions, about 4,000 auxiliary light infantry. 1,000 crack Gaullic horsemen, 3,000 western Asian horsemen. 6,000 Armenian cavalry arrived with Artabazes, their king. Artabazes implored Crassus to take the army through his own country, which would provide them with ample provisions and suitable terrain as defense from Parthian cavalry. The priests in Crassus' troupe implored him not to go at all. However, Crassus, desiring a more direct route foolishly choose a path strait through Mesopotamia with Seleucia city and Ctesiphon as his objectives. At this, the Armenian and his cavalry returned home.
That spring Crassus took his army across the Euphrates River near the town of Zeugma during a heavy thunder storm. Scouts found none of the enemy, but noticed numerous horse tracks. He was then joined by 6,000 Nabataen Arab cavalry. Their chieftain, Ariamnes, was actually in the employ of the Parthians. Ariamnes lied, saying that Parthian forces were currently fleeing the area and the only resistance might come from an advance guard under the general, Surena. Crassus was convinced of the need for haste and decided to continue along the less secure desert route. In actuality the Parthian King, Orodes II (or Hyrodes), had split his army in two. The king lead a attack on Armenia as punishment for mobilizing with the Romans. Surena (one of the senior members of the 7 great clans of Parthia) was sent to attack the Romans. His army was comprised primarily from men from his own clan. The horse archers were from the Saka and Yue-Chi people. It is believed this force was only intended to delay the Romans as Orode finished his punitive attack and returned from Armenia.
Ariamnes lead the Romans away from the river. At first the march was pleasant and easy, but they soon were amidst the featureless desert. They continued through the treeless, waterless waste. At this point of low morale, they received messenger from Armenia informing them that it was impossible for Artabazes to send any help as he was too busy defending his own country. His advise was for Crassus to turn back and join forces in Armenia, or at least leave the desert for the defenses of more mountainous ground. Crassus, however, was only angered by this and swore to punish Artabazes for this. A staff officer, Cassius, and other officers suspected Ariamnes' treachery and began to argue with Crassus, but this only angered him more. The Arab stayed long enough to convince Crassus to quicken their pace. Then he and his cavalry left the Romans claiming they intended to find ways to disrupt the enemy.
As the Romans approached the town of Carrhae (modern-day Haran) their scouts raced back, saying that most of their fellows had been killed and the Parthians were at hand in full force and preparing to give battle. Astonished at this, Crassus scarcely knew what to do. His troops were in disarray as they had been marching at such a great speed. Cassius advised the panicked general to open up the ranks and form a line across the plain, placing the cavalry on each wing to prevent them from being surrounded. As this order was being carried out Crassus changed his mind and decided to form a giant hollow square with 12 cohorts on each side with cavalry and light infantry support. Cassius commanded one wing, Cassus' son, Publius another and Crassus himself went to the middle of the square. They marched forward and as they approached the Ballisur stream Crassus was advised to make camp, rest his men and wait till day to assess the strength of the enemy. He would have none of this, giving his troops only enough time to eat before charging them forward at the enemy. When they did see the Parthians they were not impressed. Surena had ordered his main force of heavy cavalry behind the front ranks and told them to hide their armor under coats and skins. When the Romans were about ready to engage the Parthians gave the signal for battle and the dreaded cataphracts uncovered their magnificent armor.
Surena's first plan was to break the Roman lines with his 1,000 cataphracts, but when he realized the depth of the Romans he called back the cavalry. At this the Roman light infantry rushed out only to be chased back by a hail of arrows. The Parthian horse archers began to surround the square, pouring a steady stream of arrows into the densely packed ranks. The arrows were of such strength that they could punch through armor and shields. The Romans waited for the arrow supply to run out. This hope was dashed when they saw Surena had brought a camel train carrying a great quantity of arrows.
Crassus saw that his rear was about to be attacked. He ordered his son, Publius to take 1,300 Gaulic horsemen, 500 archers and 8 cohorts to attack the Parthian archers. The Parthians galloped away with this Roman attack force in chase. Once Publius was far enough away from the main body of Romans, the horse archers wheeled about and were joined by a larger number of Parthians including the cataphracts.
Publius lead his Gauls on the cataphracts. Because their spears could not penetrate the cataphract armor, the frenzied Gauls grabbed on the enemy lances, pulled them to the ground, and also leaped underneath the Parthian horses to attack their exposed bellies. They even drove their own horses onto the lances. Most of the Gauls lost their mounts and were forced to retreat with Publius to a small hillock where they were surrounded. Publius ordered his armor-bearer to kill him. After the fighting the Parthians took Publius' head and 500 prisoners.
All the while Crassus was pleased that the attack on his rear had slackened. He order his men to form up in a conventional battle formation and relocated his army to sloping ground. He then got word of what was happening to his son's force. He sent no support, but began to advance. This was when the Parthians rode in with his son's head on a pike. The advance was stopped by the archers and cataphracts. Crassus had completely lost his senses by now. His lieutenant Octavius and Cassius took over and decided to retreat that night, leaving the wounded behind. When the cavalry heard this they left immediately, stopping at Carrahe long enough only to tell the men there that Crassus had fought a great battle. They then raced on to Zeugma. The Parthians watched the retreat and waited till daybreak to ride in and slaughter the Roman wounded. Plutarch wrote that no fewer than 4,000 died in this way. Some time later, A lieutenant, Varguntinus, and his 4 cohorts had strayed from the main body of Romans and were surrounded. All were killed with the exception of 20 men who were allowed to go for showing such courage in trying to fight past the Parthians.
Surena soon learned that Crassus and his men had reached the safety of the Carrhae town walls. The next day when the Parthians arrived there, Crassus again decided to retreat at night. Again, a spy lead the Romans through the worst possible route. They were trapped in marsh. Surena offered peace to the Romans if Crassus came to parlay. Tired and afraid, the legions demanded Crassus go, threatening his life if he did not. At the meeting there was a scuffle and Crassus was killed. Some of the Romans surrendered most were hunted down and killed. In the end 20,000 Romans died and 10,000 were taken prisoner and settled in the territory of Sagdia. The captured Legionary standard were held as prizes in the temples of Parthia.References:
1. Plutarch's Lives Volume 1 by Plutarch. Arthur Hugh Clough (Editor), John Dryden (Translator)
2. Rome's Enemies (3): Parthians and Sassanid Persians by Peter Wilcox