Ninth king of Portugal and last of the House of Burgundy, whose wars with Castile and lack of a male heir triggered the 1383–1385 succession crisis.
Ferdinand I, ninth king of Portugal, was the last ruler of the House of Burgundy that had governed since Afonso I. His reign was dominated by three wars against Castile — the Fernandine Wars — fought over his claim to the Castilian throne after the murder of Peter of Castile, and by his controversial marriage to the Portuguese noblewoman Leonor Teles.
His reign left the kingdom exhausted by war but strengthened by commercial and defensive works, including the great Fernandine Walls of Lisbon. When he died in 1383 leaving only a daughter, Beatrice, married to John I of Castile, the prospect of Portugal passing to the Castilian crown provoked the succession crisis known as the Interregnum of 1383–1385.
Ferdinand was born in 1345, the legitimate son and heir of Peter I. He came to the throne in 1367 as the last legitimate male heir of the Burgundian line. When the male line of Castile's ruling house was extinguished by the killing of Peter of Castile in 1369, Ferdinand — as a great-grandson of a Castilian king — advanced a claim to the Castilian throne, drawing Portugal into a long and draining rivalry.
Ferdinand I is remembered through two contrasting bynames — "the Handsome" (o Formoso) and "the Inconstant" (o Inconstante) — and the second captures the judgement of the chronicler Fernão Lopes, who portrayed a king of shifting purpose and poor political judgement. Lopes presents a ruler repeatedly drawn into wars he could not win, changing alliances between Castile, Aragon, and England, and dominated by his wife Leonor Teles and her favourites.
His marriage to Leonor Teles, whom he took from another husband, scandalised the kingdom and became central to the hostile memory of his reign, as her influence and that of her lover the Count Andeiro were blamed for misgovernment. Yet the same king pursued real and far-sighted policies — encouraging trade, protecting shipping, and fortifying Lisbon. The portrait that survives is of a well-meaning but irresolute ruler whose inconstancy and disputed marriage helped bring the dynasty to its crisis.
Ferdinand fought three wars against Castile between 1369 and 1382 to press his claim to the Castilian throne, allying at various times with the Crown of Aragon, Granada, and England. The wars brought Castilian armies into Portugal, including the sack of the outskirts of Lisbon, and ended without securing his claim, leaving the kingdom weakened and its finances strained.
To defend the capital, Ferdinand built the Fernandine Walls, a new and greatly enlarged ring of fortifications around Lisbon that reflected the city's growth as a commercial port. He also legislated to encourage agriculture and maritime trade, measures aimed at repairing the economic damage of continual war. His English alliance in the last war foreshadowed the Anglo-Portuguese partnership that his successor would formalise.
Ferdinand died in 1383 leaving no legitimate son. His only surviving heir was his daughter Beatrice, married to John I of Castile, which raised the immediate prospect that the crown of Portugal would pass to the king of Castile. The regency of the widowed Leonor Teles was widely distrusted, and within months the kingdom slid into the crisis of the Interregnum.
Ferdinand I was the last king of the House of Burgundy, and his reign's failures — the fruitless wars, the disputed marriage, and above all his death without a male heir — set the stage for the 1383–1385 Interregnum and the rise of a new dynasty. His Fernandine Walls and commercial legislation, however, marked the growing importance of Lisbon and of maritime trade that would define Portugal's future under the House of Aviz.