An Algarve-centred rebellion by a Sufi sect, the al-Muridin - aided by Almohad arms - destabilised the region and set up a number of 'second taifa kingdoms' in Silves, Mértola and Tavira in the south. As well as being on the front line against the Christians, the São Mamede mountains are likely to have been on the northern edges of troop movements by the al-Muridin leader, Ibn Qasi and Almohad forces, against Almoravid centres of government (from 1146 to 1151). Indeed, collaboration and intrigue between Ibn Qasi, the Almohads, and a new Christian power - the fledgling Portugal, under Alfonso I of Portugal - is likely to have weakened the defensibility of the entire Tagus basin.