The Second Mithridatic War, 83-82 B.C., was a short-lived conflict largely caused by the ambition of Lucius Licinius Murena, the Roman governor of Asia after the end of the First Mithridatic War. Murena had been left in Asia Minor by Sulla, with orders to continue the reorganisation of the Roman province, which had been overrun by Mithridates VI of Pontus during the first war. The two men had rather different views of the future of relations between Rome and Pontus. Sulla wanted to maintain the peace with Mithridates, but Murena is said to have been looking for a chance to resume the war, hoping to win himself a triumph.
Murena would not have to wait long to find a pretext for war. At the end of the first war, Mithridates was faced with revolts in Colchis and around the Cimmerian Bosporus. The problems in Colchis were at least temporarily solved when Mithridates appointed his son Mithridates Philopator Philadelphus as regent in the area, but the Bosporan rebellion was more serious, and Mithridates was forced to prepare for a major military expedition across the Black Sea.
Murena did have some reasons to be suspicious of Mithridates's intentions. One of the terms of the peace of Dardanus was that Mithridates was to pull out of Cappadocia, and allow the restoration of King Ariobarzanes. By 83 B.C. Mithridates had pulled out of most, but not all of Cappadocia, so it was possible that his new army was to be used there. Murena's suspicions were also raised by the arrival of Mithridates's former general Archelaus, who had fallen out of favour in Pontus. Archelaus supported the idea that Mithridates was planning to attack the Romans, and convinced Murena to attack first.
Murena's first campaign took him through Cappadocia and to the Pontic town of Comana. Mithridates responded by sending ambassadors to Murena, to appeal to the authority of the peace treaty. Murena replied that he saw no treaty. This would remain a weakness of Mithridates's position until the outbreak of the Third Mithridatic War - no written version of the treaty had yet been produced, and after the death of Sulla the senate refused to ratify it. After the meeting with the ambassadors Murena plundered Comana, and its wealthy temple, then went into winter quarters in Cappadocia.
The appeal to Murena having failed, Mithridates then sent embassies to the Senate and to Sulla. While these embassies were on their way, Murena carried out a large scale raid into Pontus. Appian states that he captured 400 villages belonging to Mithridates without opposition, and then returned to Phrygia and Galatia.
The reply from the Senate arrived first. Quintus Calidius publicly ordered Murena not to attack the king, as the treaty was still intact, but appears to have also had a private, less peaceful message. In 82 B.C. Murena launched a second raid into Pontus, and this time, believing that the Romans had actually declared war, Mithridates reacted. An army under Gordius, a Cappadocian noble and one of Mithridates's nobles, carried out his own raid into Roman territory, and then faced up to Murena, probably on the Halys River.
The two armies faced each other across the river, until Mithridates arrived with a larger army. Mithridates then attacked across the river, inflicting a defeat on Murena, who was forced to flee over the mountains to Phrygia.
The war was now ended by a message from Sulla. His envoy, Aulus Gabinius, arrived in Asia Minor and ordered Murena not to attack Mithridates, and to arrange for a reconciliation between Mithridates and Ariobarzanes. This meeting went rather in Mithridates's favour. Ariobarzanes was engaged to Mithridates's four year old daughter, but at the same time Mithridates acquired another strip of Cappadocia. Despite having suffered a serious defeat, Murena was eventually rewarded with his triumph, one of the least deserved to be handed out.
This second peace between Rome and Pontus only lasted for eight years. Sulla died in 78 B.C., removing one of the only voices for peace in Rome. Both sides began to prepare for the upcoming war, which was triggered by the death in 75 or 74 B.C. of Nicomedes IV of Bithynia, who left his kingdom to the Roman republic.