After defeating Pompey and the optimates at Pharsalus, Julius Caesar pursued his opponents to Asia Minor and then to Egypt. In the Roman province of Asia he left Calvinus in command with an army including the 36th Legion, mainly made up of veterans from Pompey's disbanded legions. With Caesar preoccupied in Egypt and the Roman Republic in the midst of a civil war, Pharnaces saw an opportunity to expand his Kingdom of the Bosphorus into his father's old Pontic empire. In 48 BCE he invaded Cappadocia, Bithynia, and Armenia Parva.

Calvinus brought his army to within seven miles of Nicopolis and, avoiding an ambush set by Pharnaces, deployed his army. Pharnaces now retired to the city and awaited a further Roman advance. Calvinus moved his army closer to Nicopolis and built another camp. Pharnaces intercepted a couple of messengers from Caesar requesting reinforcements from Calvinus. He released them hoping the message would cause the Romans to either withdraw or commit to a disadvantageous battle.

Calvinus ordered his men to attack and his lines advanced on the enemy. The 36th defeated their opponents and started to attack the Pontic centre across the trench. Unfortunately for Calvinus, these were the only soldiers in his army to have any success. His recently recruited troops on the left broke and fled after a counterattack. Although the 36th Legion escaped with light losses, just 250 casualties, Calvinus had lost nearly two thirds of his army by the time he had fully disengaged.