The Almohads' involvement in Al-Andalus began as early as 1145, when Ali ibn Isa ibn Maymun, the Almoravid naval commander of Cadiz, defected to 'Abd al-Mu'min. In the same year, Ibn Qasi, the ruler of Silves, was one of the first Andalusi leaders to appeal for Almohad intervention in Al-Andalus in order to stop the advance of the Christian kingdoms, whom the faltering Almoravids were unable to contain. In 1147 Abd al-Mu'min sent a military force led by another Almoravid defector, Abu Ishaq Barraz, who captured Algeciras and Tarifa before moving west to Niebla, Badajoz, and the Algarve. The Almoravids in Seville were besieged in 1147 until the city was captured in 1148 with local support.