On 14 August 1415, he accompanied his father and brothers Edward and Henry for the Battle of Ceuta in Morocco. His mother had died the previous month, giving each of her sons on her deathbed an arming sword she had ordered forged for them. Peter refused to be knighted before showing valour in battle, and he was knighted along with his brothers the following day; he was also created Duke of Coimbra. His younger brother Henry was made Duke of Viseu. These were the first dukedoms created in Portugal.