The Battle of River Leça was a military encounter between a 6,800 men strong Portuguese force led by João Ramalho and Pedro, Count of Trastámara, a Castillian noble who was on the side of Portugal, and the smaller castillian contingent led by the Archbishop of Santiago sent by John I of Castile to conquer Porto. The Portuguese forces, although smaller at start, received significant reinforcements from Lisbon (that was being besieged at the time) just before the battle and were hence able to prevent a Castilian attack on Porto.