The Battle of Kleidion (Ancient Greek: Κλειδίον; or Clidium, after the medieval name of the village of Klyuch, lit. 'key'; also known as the Battle of Belasitsa) took place on 29 July 1014, between the Byzantine Empire and the Bulgarian Empire. It was the culmination of the nearly half-century struggle between the Byzantine Emperor Basil II and the Bulgarian emperor Samuel in the late 10th and early 11th centuries. The result was a decisive Byzantine victory.
The battle took place in the valley between the mountains of Belasitsa and Ograzhden, near the modern Bulgarian village of Klyuch. The decisive encounter occurred on 29 July with an attack in the rear by a force under the Byzantine general Nikephoros Xiphias, who had infiltrated the Bulgarian positions.