In summer 69 BC, Roman legions under the command of Lucullus invaded Armenia and rapidly advanced towards the heart of the country. At the time being in the southern regions of Armenia, Tigran II the Great sent a 3,000 cavalry under the command of Meruzhan to stop the Romans.
Having covered a large distance, the fatigued Armenian cavalry clashed with the Romans in an unequal battle. Armenians suffered heavy losses and their commander Meruzhan was killed. Romans shorty besieged Tigranocerta, the capital of the Armenian Kingdom. Along with his 6,000-guardsman army, Tigran managed to break through the Roman troops into the city to evacuate the royal family and the treasury of the kingdom.
On October 6, 69 BC, a large battle broke out near Tigranocerta, in which the Romans forced the Armenians to retreat. The besiegement of the capital would last several months. The treason of Greek mercenaries and other foreigners living in Tigranocerta who opened the gates of the city for the Romans contributed to the fall of the capital.
Having severely plundered Tigranocerta, Lucullus decided to capture Artashat, the second capital of Armenia, and marched towards the north. Meanwhile, Tigran and Mithridates VI of Pontus were gathering and training new troops. Tigran followed the old tactics of the Armenian army. Avoiding large clashes, the Armenian units in small battles eliminated the lesser detachments of the Romans and hampered the supply chain of the Roman army. Even though this tactic effectively harassed the Romans, it didn’t manage to stop them.
Lucullus stubbornly lead the exhausted legions forward, encouraging them with the loot that was waiting for them in Artashat. The threat of the city’s loss forced Tigran to engage in a large battle against the Romans near the crossing of Aratsani River in September 68 BC. This time, the well-trained and organized Armenian army defeated the Romans, who, suffering great losses, were forced to leave Armenia.
Amplifying the success, Armenians also drove the Romans out of the southern regions of Armenia, including Mesopotamia. In the meantime, Mithridates invaded Pontus and won his kingdom back. Romans avoided to fight against both the Romans and Armenians, but this didn’t prevent another major battle in Pontus, in which the Romans were yet again defeated.
These victories allowed Tigran to focus on the development of his kingdom for a short time. However, the unsuccessful coup attempt lead by Tigran’s son Tigran resulted in inter-clan clashes within Armenia, disturbing the plans of the king, even though his son’s uprising was suppressed. In the end, the king’s son fled to Parthia to find shelter.