Battle of Ani

The Battle of Ani was fought between the forces of Vahram Pahlavouni and the Byzantine Empire in 1042. The Byzantine Empire was soundly defeated, with up to 20,000 dead.

Background
Vahram selected a body of 30,000 infantry and 20,000 cavalry, forming three divisions, which fought against the Byzantines. A battle ensued in which the invaders were routed with great slaughter. The fight was so ferocious that the effusion of blood flowing into the Akhurian River is said to have coloured its waters completely red.

The Byzantines left 20,000 dead behind. This victory allowed Vahram Pahlavuni along with Catholicos Petros Getadarts to crown Gagik II king of Armenia and subsequently take the fortress of Ani, which had been in the hands of Vest Sarkis.

Source

 * F. Macler. Armenia, The Kingdom of the Bagratides. The Cambridge Ancient History, Vol. IV.