The Battle of Cerneja took place at Cernesa (Cerneja), an unidentified site in Galicia, in 1139/40, between the County of Portugal and the Kingdom of León. In the aftermath of the Portuguese victory at the Battle of São Mamede (1128), the Portuguese count, Afonso Henriques, began a concerted effort to establish his independence, growing increasingly uncomfortable sharing power with his mother, Countess Theresa, who was supported by the Galician nobility and her lover, Fernando Pérez de Traba. The Chronica Adefonsi imperatoris notes that "prior to this, the Portuguese monarch had come to Galicia several times, but always he had been driven back by Fernando Pérez and Rodrigo Vélaz and other Galician leaders. Often he was forced to return to Portugal dishonored." Between 1137, when he signed