First Fernandine War
Part of Fernandine Wars
Ferdinand I of Portugal
Date 1369–1371 Location Iberian Peninsula Result Treaty of Alcoutim Treaty of Tui (1372)[7]
Belligerents
Portuguese House of Burgundy Kingdom of Portugal and the Algarve Kingdom of Galicia Zamoran Rebels[1] Crown of Aragon[2] Emirate of Granada[3][4]	House of Trastámara Realm of Castile White Company[5][6]
Commanders and leaders
Ferdinand I of Portugal Peter IV of Aragon[8] Lanzarote Pessanha Ferdinand Alfonso of Valencia Fernando Ruiz de Castro Vasco Gomes de Abreu Deu-la-Deu Martins[9][10] John Alfonso of Zamora Muhammad V of Granada[11] Ferdinand of Olivença[12]	Henry of Trastámara Ambrosio Bocanegra Juana Manuel of Villena Pedro Rodrigues Sarmento Pedro Manrique Bertrand du Guesclin[13][14]
Strength
Unknown	Unknown
Casualties and losses
Unknown	Unknown

The First Fernandine War was the initial conflict in the series of wars between the Kingdom of Portugal and the Realm of Castile during the late 14th century. It commenced in 1369 following the assassination of King Pedro I of Castile and concluded in 1371 with the signing of the Treaty of Alcoutim.^[15]

The war was primarily a dynastic struggle, with King Ferdinand I of Portugal asserting his claim to the Castilian throne after the murder of his cousin, King Pedro I. This claim was contested by Henry II of Castile, who had seized the throne through assassination. The conflict was marked by border skirmishes, sieges, and naval engagements.

In 1370, Portuguese forces Sacked the Andalusian port city of Cádiz to stop Castilian maritime activities and assert Portuguese naval presence in the region. The raid resulted in significant damage to the city and big Profit for the Portuguese and their naval operations.^[16]

In the same year, an armada headed for Seville consisting of thirty-two galleys and thirty ships. That were under the command of Admiral Lançarote Pessanha and Captain-Major João Focim, a Castilian knight exiled in Portugal Launched a naval blockade on Seville. The main objective was to immobilize the Castilian fleet and block supplies to Seville.^[17]

In 1370, Castilian forces laid siege to the town of Monção, located in northern Portugal. The defenders, led by Captain Vasco Gomes de Abreu and his wife, Deu-la-Deu Martins, faced dire conditions. According to local legend, Deu-la-Deu Martins baked a small amount of bread and threw it over the walls to deceive the besiegers into thinking the town had ample supplies. This ruse led to the lifting of the siege and a Portuguese victory.^[18][19][20]

The Battle of Porto de Bois was the Decisive last engagement during the First Fernandine War. Portuguese and Castilian armies clashed near the Pambre River. The Portuguese and their Galician Supporters were Crushed by the Castillan and French Coalition, ending the First Fernandine War^[21] ```

The First Fernandine War concluded in 1371 with the signing of the Treaty of Alcoutim, which temporarily halted hostilities between Portugal and Castile. However, Portugal betrayed the Castilian treaty, eventually leading to the Second Fernandine War in 1372.^[22]