In the Battle of Tigranocerta in 69 BCE the Roman army
under general Lucullus defeated an Armenian army that was much larger.
Military historians laud it as an example of Lucullus' generalship.
The battle was part of the Third Mithridatic War, in which Rome fought against the kingdoms of Pontus and Armenia for control over the north and east of Asia Minor. Lucullus had in 73 BCE defeated Mithridates VI, king of Pontus, who had found shelter with his son-in-law Tigranes II, king of Armenia. Though he had no authorization from Rome, Lucullus crossed the Euphrates river into Armenia and headed for Tigranocerta, the recently founded capital of Armenia. Tigranes was astounded by the speed of the Roman advance and sent a force of 2,000 - 3,000 cavalry to slow them down, but these were routed by the Roman cavalry, only 1,600 strong. Tigranes retreated to hastily recruit an army, but Lucullus did not pursue because he did not want Tigranocerta unconquered in his rear, so he started to besiege it. Tigranocerta was not yet finished but already had massive walls. Roman siege engines and miners that crept up to these walls were driven off by naphtha thrown down by the defenders.
While the siege continued, Tigranes returned with a relief army. The size of the opposing forces is unclear, the historical accounts being clearly very unreliable. Lucullus had access to seven legions, but brought only part with him, possibly 12,000 heavy infantry, 4,000 auxiliaries and 2,000 cavalry. Tigranes brought a much larger army, maybe 40,000 infantry and 10,000 - 15,000 cavalry, including many cataphracts.
Lucullus left part of his army behind to continue the siege and marched his main force northeast to meet Tigranes. The two forces lined up on opposite sides of the Batman-Su river southwest of the city. Some superstitious Romans tried to dissuade their general from attacking, reminding him that it was the anniversary of the disastrous Romand defeat at Arausio. But he ignored them and went on. He deployed his army in a wide single line, in order not to be outflanked. He wanted to make a running charge against the enemy to give them as little time as possible to fire missiles. But at the last moment he realized that the Armeninan cataphracts were a bigger threat and ordered his own cavalry to distract them. They first attacked, then withdrew, luring many easterners away.
Two Roman cohorts crossed the river at a ford and after that Lucullus personally led the charge onto a hill where the left flank of the Armenians was stationed. They attacked the cataphracts first, slicing at the legs of the horses, which were unarmored. The other Armenians, mostly inexperienced levies from various parts of the country, where thrown into confusion by the encircling move. When Tigranes gave up and ran away to the north with the baggage train, the whole army collapsed. Lucullus had his troops chase the enemy for more than 20 kilometers until nightfall.
Losses on the Roman side were slight but high (5,000?) among the Armenians, though again numbers are very vague. The besieged population in the city, deprived of hope, opened the gates to the Romans, who started plundering. Though Tigranes lost an important city and much territory, he was not yet beaten. Mutiny among the Roman soldiers later in the campaign weakened Lucullus' position and eventually he lost all he had gained in the battle.