The battle of Zela (May 47 BC) saw Caesar defeat Pharnaces, king of the Cimmerian Bosporus, so quickly that it inspired his most famous quote, ‘Veni, vidi, vici’, or ‘I came, I saw, I conquered’.
Pharnaces was the son of Mithridates the Great of Pontus. Towards the end of the Third Mithridatic War, Mithridates had fled to his last remaining holdings, in the Cimmerian Bosporus (parts of the Crimea and the lands to its east), but he had lost control of the area, and had eventually committed suicide after Pharnaces rebelled against him. Pharnaces sent his father’s body to Pompey the Great, who had confirmed him as king of the Cimmerian Bosporus.
For some time Pharnaces was happy with his new kingdom, but in the aftermath of Caesar’s victory over Pompey at Pharsalus, he decided to try and regain control of his father’s empire. He successfully advanced around the east coast of the Black Sea, conquering Colchis, Lesser Armenia, part of Cappadocia, and parts of the Roman province of Bithynia and Pontus. Caesar’s governor of Asia, Domitius Calvinus, led an army made up of one Roman and three Allied legions to deal with the threat, but suffered a heavy defeat at Nicopolis and had to retreat west into the Roman province of Asia. Pharnaces was free to invade the rest of Pontus, taking advantage of Caesar’s absence in Alexandria.
Things began to turn against Pharnaces after Caesar’s victory at the battle of the Nile. This allowed him to settle the situation in Egypt, and then move north to Syria, where he caught up with the affairs of the Roman world. His most serious problem was the major Republican army that had formed in North Africa, but he decided to deal with Pharnaces first. After reaching Antioch, he crossed over into Asia Minor, and then advanced north towards Pontus.
Caesar didn’t have many troops with him when he reached Pontus. He had the veteran 6th legion, but that was reduced to under 1,000 men. According to the Alexandrian War his other troops consisted of a legion provided by Deiotarus of Galicia and Cappadocia, and two other legions that had fought at Nicopolis. The Romans had four legions at that battle - their own 36th legion, one from Pontus and two provided by Deiotarus, and it isn’t clear which two of these legions were now with Caesar.
As Caesar approached Pontus, ambassadors arrived from Pharnaces, offering to submit to all of Caesar’s commands. Caesar demanded that he retreat from Pontus and restore everything that he had looted. Pharnaces agreed to Caesar’s demands, but only in the expectation that Caesar would have to leave the area fairly quickly to deal with more serious problems closer to home. Pharnaces moved very slowly, and eventually Caesar decided that it was time to resort to force.
The longest account of the battle comes from the Alexandrian War, probably written by one of Caesar’s friends and officers.
The two armies clashed near the town of Zela, where Mithridates had won one of his last victories during the Third Mithridatic War. Pharnaces occupied the same camp as his father, on a high mountain three miles from the city. Caesar camped five miles away, on the far side of a narrow valley that separated the two armies, and that had been the site of Mithridates’s victory.
Caesar decided to occupy this valley, and fortify it. He gathered a large number of fascines, and then late at night moved his troops into the valley, arriving at dawn on the following morning. His plan was to defend one of the hills on the side of the valley, and use the fascines to block the valley itself, making it difficult for Pharnaces to take advantage of his presumably superior numbers to attack.
On the following morning, while the Romans were still busily fortifying the valley, Pharnaces moved out of his camp, drew his army up in line of battle, and then much to Caesar’s surprise advanced to attack. At first the surprise attack gained some success, with Pharnaces’s scythed chariots doing damage to the disorganised Romans, but they were soon driven off with darts, and Caesar’s men were able to form up before the enemy infantry arrived.
Along most of the line, where Pharnaces’s men clashed with Roman allies, the battle was prolonged and hard fought. However on the Roman right the Sixth Legion soon defeated their opponents. Defeat soon spread along Pharnaces’s line, and his troops turned and fled back across the valley, heading for their original camp. Many were killed during this pursuit, and others were forced to abandon their weapons in order to escape. They were thus unable to defend their camp, which fell to the Romans. However the attack on the camp did allow Pharnaces to escape.
Caesar was especially happy with the speed of this victory, which had brought a potentially very dangerous war to an unexpectedly rapid end. Pharnaces managed to escape to his original kingdom, but Caesar had no interest in following him to the Crimea. In the end it didn’t matter, as Pharnaces was killed in battle while attempting to regain control of his original kingdom.
Appian provides a different account of the battle. In his version Pharnaces became alarmed as Caesar approached, and began to send ambassadors asking for peace. They offered Caesar a gold crown and the hand of Pharnaces’s daughter in marriage. Caesar advanced ahead of his army, accompanied by 1,000 cavalry, met up with the ambassadors, and appeared to be escorting them back to Pharnaces’s camp. When he reached the camp he said ‘Why should I not take instant vengeance on this parricide?’, and attacked with his cavalry. Pharnaces turned and fled, and his army fell apart. His report back to Rome read ‘Veni, vidi, vici’, or ‘I came, I saw, I conquered’. This account doesn’t fit with the large battle reported in the Alexandrian War or by Plutarch, and isn’t terribly convincing.
In the aftermath of this victory Caesar returned to Rome, before heading to Africa, where he defeated the last major Republican army at Thapsus (February 47 BC).