On April 3, 1367, the Battle of Nájera, also known as the Battle of Navarrete, was fought in La Rioja, Castile, between the forces of King Pedro I of Castile, supported by the English under Edward the Black Prince, and those of his half-brother Henry of Trastámara, backed by French troops. The battle resulted in a decisive victory for Pedro and the English, but it proved pyrrhic, as Pedro's harsh reprisals and failure to repay his debts alienated his allies and sowed the seeds of his eventual downfall.

The Battle of Nájera was one of the most significant engagements of the Hundred Years' War fought on Spanish soil, and it was vividly described by the chronicler Jean Froissart, whose account became a touchstone for later historical and poetic treatments. The battle's dramatic reversal—a victory that led to ultimate defeat—made it a favorite subject for moralizing poets and dramatists, who used it as an example of the fickleness of fortune. The battle's legacy can be traced in Spanish epic poetry and in the English tradition of historical verse that celebrated the martial exploits of the Black Prince.