In February 1476, the Portuguese army, reinforced by troops brought by John II of Portugal, son of Afonso V, left its base in Toro and surrounded Ferdinand in Zamora. The siege took a worse toll on the Portuguese than on those under siege because of the Castilian winter, and on March 1, Afonso V withdrew back towards Toro. Ferdinand and his troops launched a pursuit and caught up to the Portuguese one league (about 5 km) from Toro, and combat began.