Al-Walid I began the next stage of Islamic conquests. Under him the early Islamic empire reached its farthest extent. He reconquered parts of Egypt from the Byzantine Empire and moved on into Carthage and across to the west of North Africa. Muslim armies under Tariq ibn Ziyad crossed the Strait of Gibraltar and began to conquer the Iberian Peninsula using North African Berber armies. The Visigoths of the Iberian Peninsula were defeated when the Umayyad conquered Lisbon. The Iberian Peninsula was the farthest extent of Islamic control of Europe (they were stopped at the Battle of Tours). In the east, Islamic armies under Muhammad bin Qasim made it as far as the Indus Valley. Under Al-Walid, the caliphate empire stretched from the Iberian Peninsula to India. Al-Hajjaj ibn Yusuf played a crucial role in the organization and selection of military commanders. Al-Walid paid great attention to the expansion of an organized military, building the strongest navy in the Umayyad era., This tactic was crucial for the expansion to the Iberian Peninsula. His reign is considered to be the apex of Islamic power.