In the spring of 67 BC, most Roman troops had left Pontus for Mesopotamia. Two Fimbrianlegions (around 12 thousand men) refused to leave and fell easy prey for Mithridates. The Roman legatus mobilized slaves to fight alongside legionnaires, but the Persians won the first battle. The Romans lost around five hundred men and retreated. Mithridates was wounded in the face with an arrow but recovered in a few days.
The battle of Zela, the second encounter of the 67 BC campaign, was a Roman attempt to regain control after their tactical loss to Mithridates. It was preceded by a freak tornado; both sides interpreted the omen as a call to a final, decisive battle. The Romans attacked the Zela camp at night. The Persians repelled the first strike and drove the Romans back into their trenches which were soon "clogged with dead Romans". Mithridates was critically wounded again, and once again a shaman by the name of Agari healed the king with snake venom. Only hours after the near-fatal wound, Mithridates was back in his saddle. By this time, the Romans had already fled, leaving seven thousand dead, including 24 tribunes and 150 centurions.