In late 788 or early 789, the Byzantine Empire invaded southern Italy in an effort to detach the kingdom of the Lombards from the Frankish domination and restore the exiled king Adelchis. The expeditionary army, supported by the Sicilian theme, was defeated in a major battle by a combined force of Lombards and Franks under Duke Grimoald III of Benevento.
The cause of the war was the breakdown in 788 of the proposed marriage between the Emperor Constantine VI, still under the regency of his mother, Irene, and Rotrude, the daughter of the Frankish king Charlemagne. Following the war, relations between the two empires were not re-established until 797.