The battle of Nicopolis (48 BC) saw Pharnaces, the son of Mithridates the Great of Pontus, defeat a Roman army that was attempting to stop him taking advantage of Caesar’s absence in Egypt to regain control part of his father’s old Empire.
After his defeat in the Third Mithridatic War, Mithridates fled to his last intact possession, the Cimmerian Bosporus (parts of Crimea and the Taman peninsula, to the east of the Crimea). However he soon alienated his supporters, and was overthrown by his son Pharnaces. Pharnaces sent his father’s body to Pompey, and was allowed to stay on as King of the Cimmerian Bosporus.
For some time Pharnaces remained content with his reduced kingdom, but in 49 BC the Great Roman Civil War broke out. The fighting soon moved to the Balkans, and in 48 BC Pompey was defeated at Pharsalus. He fled to Egypt, followed by Caesar, leaving an apparent power vacuum in Asia Minor. The Governor of Asia, Domitius Calvinus, had three legions, but soon had to send two to try and rescue Egypt, who was trapped in Alexandria.
Pharnaces decided to try and take advantage of the absence of Caesar to re-establish his father’s empire. He quickly overran Colchis, on the eastern shores of the Black Sea, and then advanced south into Asia Minor. He was able to seize Lesser Armenia (the area on the south-eastern shore of the Black Sea), parts of Cappadocia (in central-eastern Asia Minor), and parts of the Roman province of Bithynia and Pontus, which took up the rest of the south coast of the Black Sea.
Pharnaces now threatened King Deiotarus of Galatia and Lesser Armenia, a former ally of Pompey. He asked Calvinus for aid, arguing that Pharnaces’s conquests made it impossible for him or King Ariobarzenes of Cappadocia to keep the promises they had made to Caesar. Calvinus decided to confront Pharnaces. He sent ambassadors to order him to withdraw from Armenia and Cappadocia, and then joined his army. Two legions had to be sent to Egypt, but he kept the 36th Legion to lead against Pharnaces. He was also joined b y two legions that had been raised by Deiotarus and 200 cavalry, 100 from each of the kings. He also ordered a newly raised legion to join him from Pontus. The combined army met up at Comana (probably the city in Cappadocia).
Calvinus’s ambassadors returned with a message from Pharnaces. He had withdrawn from Cappadocia, but insisted on keeping Lesser Armenia, claiming it by right of inheritance. He claimed he was willing to submit to Caesar’s judgement. Calvinus rejected this suggestion, and advanced towards Lesser Armenia. Eventually he reached Nicopolis in Lesser Armenia and camped seven miles from the city. Between him and Nicopolis was a narrow pass, where Pharnaces was preparing to ambush the Romans. He also placed a large number of cattle in the pass, so that if the Romans advanced as friends they wouldn’t suspect an ambush, and if they advanced as enemies they might disperse to pillage the cattle. At the same time he sent more ambassadors to Calvinus, requesting peace. However this backfired, as Calvinus remained in his camp for longer than expected, reducing the chance of an ambush remaining a surprise. Pharnaces decided to withdraw to Nicopolis.
Calvinus advanced through the pass without any problems, and camped outside Nicopolis, where his men fortified their camp. Pharnacus drew up his army outside the city, with his main force in a single line, and with triple bodies of reserves on each flank. Calvinus ordered some of his troops watch Pharnacus, while the rest completed the camp.
Pharnaces was now given a great advantage, when he captured couriers coming to Calvinus with news from Alexandria. These informed him that Caesar was in great danger, and had ordered Calvinus to come to his aid. Pharnaces decided that this made a Roman attack less likely, but just in case dug two lines of four feet deep ditches to protect the easiest approaches to Nicopolis. He then drew up his army in the gap between the ditches, with the cavalry on the wings, on the outside of the ditches.
Pharnaces had misjudged Calvinus’s reaction to the news from Egypt. Calvinus believed that he couldn’t safely withdraw without first defeating Pharnaces, and so drew up his own army ready to attack. His own 36th Legion was placed on the right. The troops from Pontus were on the left and Deiotarus’s two legions in the centre. He drew up on a very narrow front, and used the spare cohorts this freed up to support his flanks.
The two sides then advanced into contact. On the Roman right the 36th Legion defeated Pharnaces cavalry outside the ditches, drove them back to the town and then turned to attack Pharnaces’s infantry from the rear. On the left the legion from Pontus gave way, as did the supporting troops sent to reinforce them. In the centre Deiotarus’s legions gave way almost without a fight, allowing the bulk of Pharnaces’s troops to turn on the 36th Legion. This force was surrounded, but forced into a circle and retreated to a nearby mountain. Pharnaces decided not to risk attacking them in the difficult terrain, and Calvinus was able to escape with the survivors of the battle. He lost 250 men from the 36th Legion, and an unstated number from the allied forces.
In the aftermath of this victory Pharnaces advanced into Pontus and occupied the entire area. However his success would be short lived. Caesar was able to escape from his difficulties in Egypt, and eventually came north to deal with Pharnaces. When the two sides finally clashed at Zela (May 47 BC), Caesar won a very quick victory, inspiring his most famous quote - ‘Veni, vidi, vici’, or ‘I came, I saw, I conquered’.