 In 727, the Arab army, led by one of the Caliph's sons, penetrated deep into Asia Minor, sacked two Byzantine fortresses and in late July arrived before Nicaea.Despite constant attacks for 40 days, the city held firm and the Arabs withdrew 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.