The unsuccessful second siege of Constantinople (717) weakened the Umayyad dynasty and reduced their prestige. After their success in overrunning Iberia, the conquerors moved northeast across the Pyrenees. They were defeated by the Frankish leader Charles Martel at the Battle of Poitiers in 732. The Umayyads were overthrown in 750 by the Abbāsids and most of the Umayyad clan were massacred.