Battle of Alfarrobeira The Battle of Alfarrobeira ( ) took place on 20 May 1449 . It was a confrontation between the forces commanded by King Afonso V of Portugal and his uncle Afonso , Duke of Braganza , against the army of the rebellious Pedro , Duke of Coimbra . The place was Alverca do Ribatejo , near Lisbon , at the margins of the creek of Alfarrobeira . The result was the clear defeat and death of the Duke of Coimbra and the establishment of the Braganzas as the most powerful House of Portugal . The reasons for battle . After the death of King Fernando , the last of the First Dynasty , in 1383 , power fell on the regent Queen Leonor , hated by the people , and her daughter Beatrice , married to the Castilian King Juan I . Fernando ' s half - brother John , Master of Aviz , led a revolution against Queen and the Castilian King , defeating them with a smaller army in the battle of Aljubarrota . The battle became a turnpoint in Portuguese and the world ' s History , and King John I and his military aide , Constable Nuno Álvares Pereira , became immortal idols . King John I had a first illegitimate son , Afonso , and a daughter Beatrice ; after marrying Philippa of Lancaster , John of Gaunt ' s daughter , and establishing the House of Aviz , they had a first boy ( died of young age ) , a girl Isabella ( who became a famous duchess of Burgundy and Flanders ) , then five boys who were grew up under the memories of the famous battle . Edward ( Duarte ) was trained to become King , Peter ( Pedro ) , Henry ( Henrique , a . k . a . " The Navigator " ) , that was becoming powerful and famous with the military actions in Northern Africa against Muslims ; John and Fernando , the youngest , died before Alfarrobeira . For ten years Peter lived abroad . When King John I , and a few years later , King Edward , died , the crown fell on the boy Afonso V , under the regency of the Queen , an Aragonese ; the people remembered 1383 and the civil war , and rebelled against the Queen . The old Afonso , Count of Barcelos , King John ' s first son , supported the Queen . Peter ( now the eldest brother ) led a revolution with the help of his brothers , but Henry managed to establish peace through a tripartite regency between the Queen , Peter and Afonso . In the years to follow , the Queen tried a coup - d ' etat with the help of her family ; Peter , married to an Aragonese whose family fought for Castilian power against the Queen ' s family , managed to send her back to Castile , appeased older Afonso giving him the Duchy of Braganza and conquered the thrust of his sons by promising them military titles , married his daughter to the young King , and assumed the Regency , establishing himself as the most powerful man in Portugal with the help of his brother Henry . But he made mistakes , for when his two brothers John and Fernando died , he gave their military titles to his sons , and not Afonso ' s sons as promised . When young Afonso V reached his 14th birthday , he dismissed his uncle as regent , associated with Afonso ' s sons , and began to uproot Peter ' s men from their positions of power . Finally , for reasons that would be proven false later , the King marched against Peter . The battle , near Lisbon , to the North , was short , and Peter one of its first victims being killed by an arrow . Henry , King John ' s fifth son , was now first and only of the House of Aviz . Outcomes of the battle . Mistrusted by King Afonso V and the Duke of Braganza ' s sons as a member of the House of Aviz , and mistrusted by his dead brother ' s friends who never accepted his betrayal ( and rejected by his old sister Isabella , in Burgundy ) , Henry retreated to his land in Sagres , the southernmost and westernmost tip of Portugal - and Europe . There , living a secluded and religious life , he concentrated his efforts on the sailing expeditions of his men , becoming worldly renowned as discoverer of never before seen oceans and coasts ( Madeira , Azores , the African coast to Guinea , and after his death Cape of Good Hope , India , Japan , Canada , Brasil , etc . ) . Afonso V ignored the travels of his uncle and immersed himself in the battles of Castile , trying to take the throne to himself , but was defeated in the Battle of Toro by Queen Isabella the Catholic and King Fernando of Aragon . He died leaving Portugal on the brink of bankruptcy . Afonso ' s son , John II , turned his back on Castile and saw an opportunity on the ocean discoveries and expanded them , making Portugal the first intercontinental empire and becoming the most powerful King in medieval History .