The battle of Tigranocerta, 6 or 7 October 69 B.C., was a one-sided Roman victory over a massive army led by Tigranes I of Armenia, but one that the Romans were unable to take advantage of. A Roman army under the command of Lucius Licinius Lucullus invaded Armenia in 69 B.C. in an attempt to capture Mithridates VI of Pontus, who had taken refuge with his son-in-law Tigranes after suffering defeat in the first phase of the Third Mithridatic War.
Tigranes was caught out by the Roman invasion, and as Lucullus approached his new capital at Tigranocerta (probably somewhere on the borders of Armenia and Mesopotamia), Tigranes retreated into the mountains to gather his main army, leaving a token force to defend the city.
Lucullus had entered Armenia at the head of an army made up of his best troops, containing no more than 12,000 legionaries, and up to 4,000 cavalry and light troops (Plutarch gave him 16,000 infantry and 1,000 cavalry). This force was too small to effectively blockade Tigranocerta, let alone conduct a proper siege, but for once Lucullus was hoping to fight a set-piece battle.
Tigranes gathered a massive army, in many ways typical of the massive Hellenistic armies that the Romans had defeated repeatedly in the past. Appian gives him 250,000 infantry and 50,000 cavalry. Plutarch gives him 150,000 heavy infantry, some organised in Roman-style cohorts and some in phalanxes, 20,000 bowmen and slingers and 55,000 cavalry, 17,000 of whom were heavily armoured, and 35,000 supporters. Hardly surprisingly Tigranes was unimpressed with the Roman army, famously describing it as 'too small for an army, too large for an embassy', and he refused to accept Mithridates's advice not to risk a battle.
The battle started with the two armies separated by a river. Tigranes's heavily armoured cavalry was posted on his right flank. The Romans had to move to their left to cross the river, and thus attacked Tigranes's army from this flank. Lucullus sent his own cavalry to harass Tigrane's heavy cavalry, and then withdrawn, luring them into a pursuit. At the same time he led his infantry onto a hill to the right of the advancing Armenian cavalry, and then attacked them in their vulnerable flank.
The Armenian heavy cavalry turned and fled, hitting their own tightly packed infantry, who also quickly broke. Tigranes is said to have fled from the scene at the start of the rout, losing his diadem on the way. Lucullus managed to prevent his own troops from breaking to loot Tigranes's abandoned camps, and most of the slaughter took place during a pursuit that went on for fifteen miles. Tigranes lost somewhere between 10,000 and 100,000 men, most of them during this final stage of the fighting.
The battle took place too late in the year for Lucullus to risk following Tigranes into the mountains of Armenia. Instead he remained in the south, where he dismantled Tigranocerta, allowing its population to return to their original homes. In the next year he attempted to chase Tigranes to his old capital at Artaxata, but this venture ended when his legions refused to march any further into the mountains. Mithridates took advantage of this to stage an unexpected return to Pontus, where in 67 B.C. at Zela he defeated a Roman army. Lucullus was forced to abandon his campaign in Armenia, and was soon replaced by Pompey, who would finish the war.