The Battle of Lalakaon was fought in 863 between the Byzantine Empire and an invading Arab army in Paphlagonia (modern northern Turkey). The Byzantine army was led by Petronas, the uncle of Emperor Michael III (r. 842–867), although Arab sources also mention the presence of Emperor Michael. The Arabs were led by the emir of Melitene (Malatya), Umar al-Aqta (r. 830s–863).

Umar al-Aqta overcame initial Byzantine resistance to his invasion and reached the Black Sea. The Byzantines then mobilized their forces, encircling the Arab army near the Lalakaon river. The subsequent battle, ending in a Byzantine victory and the emir's death on the field, was followed by a successful Byzantine counteroffensive across the border. The Byzantine victories were decisive; the main threats to the Byzantine borderlands were eliminated, and the era of Byzantine ascendancy in the East (culminating in the 10th-century conquests) began.

The Byzantine success had another corollary: deliverance from constant Arab pressure on the eastern frontier allowed the Byzantine government to concentrate on affairs in Europe, particularly in neighboring Bulgaria.