From May 29 to September 3, 1384, the Castilian army laid siege to the city of Lisbon in an effort to crush the Portuguese resistance and assert the claims of King John I of Castile to the Portuguese throne. Despite a determined siege, the Portuguese defenders, led by John of Aviz, held out against superior forces, and the Castilians were eventually forced to withdraw due to disease and supply shortages. The failure of the siege was a major turning point in the 1383-1385 Crisis, solidifying Portuguese resolve.

The Siege of Lisbon was vividly described by chronicler Fernão Lopes, whose account emphasized the heroism of the defenders and the providential nature of their deliverance. The siege became a staple of Portuguese historical poetry, with poets celebrating the courage of the besieged and the divine intervention that frustrated the Castilian ambitions. The siege's literary legacy reinforced the theme of Portuguese exceptionalism and divine favor, a theme that would be central to the nation's epic poetry and its sense of cultural identity.