Siege of Nicaea (727)
The Siege of Nicaea of 727 (a few authors put it in 726) was an unsuccessful attempt by the Umayyads to capture the Byzantine city of Nicaea, the capital of the Opsician Theme. After forty days of siege, the Arab army abandoned the attempt and returned to the Caliphate. The successful repulsion of the attack was a major boost for Byzantine emperor Leo III the Isaurian's recently initiated campaign to abolish the veneration of icons in the Empire; Leo claimed it as evidence of divine favour for his policy.
Sources