 Complete the following phrase:  The second siege of Constantinople 717 ended unsuccessfully after the intervention of Tervel of Bulgaria and weakened the Umayyad dynasty and reduced their prestige. In 722 Don Pelayo, a nobleman of Visigothic origin, formed an army of 300 Astur soldiers, to confront Munuzas Muslim troops. In the battle of Covadonga, the Astures defeated the Arab-Moors, who decided to retire. The Christian victory marked the beginning of the Reconquista and the establishment of the Kingdom of Asturias, whose first sovereign was Don Pelayo. The conquerors intended to continue their expansion in Europe and move northeast across the Pyrenees, but were defeated by the Frankish leader Charles Martel at the 