The Portuguese Interregnum

The Portuguese Interregnum
December 1383 – August 1385

The Portuguese Interregnum originated during the reign of King Ferdinand I. In 1383, Ferdinand was slowly dying. Since the king’s only son, Prince Afonso, had pre-deceased him, Ferdinand had one living child left, Princess Beatrice. As a succession crisis began to stir, the king married his daughter to King John I of neighboring Castile in May. Although they were former enemies, Ferdinand believed marriage would bring peace by uniting both kingdoms. However, many in the Portuguese nobility thought Portugal would lose its independence to Castile.

On October 22, 1383, Ferdinand I died, ending the Burgundian dynasty founded by King Afonso I in 1139. Upon his death, tensions rose between the Castilian faction, led by Queen Leonor, and the nationalist party, formed by the Portuguese nobility. To counter John I of Castile, the nobility supported Ferdinand I’s younger half-brother, John of Aviz. Although an illegitimate son of King Peter I, John was very popular amongst the Portuguese. When the nationalist party asked John to join their cause, he readily accepted.

John of Aviz had a personal reason to oppose the Castilian faction. A year prior, Queen Leonor had convinced Ferdinand I to imprison John on false charges of treason. Despite being innocent, John came close to being executed. When Leonor became regent after Ferdinand’s death, John again felt that his life was in danger. To avoid Leonor’s wrath, John and the nobility struck first, beginning the Portuguese Interregnum.

Beginning of a Civil War

In December 1383, the nationalists stormed the royal palace in Lisbon. During the invasion, Queen Leonor managed to escape and fled to Castile. With the queen gone, John of Aviz became the de-facto ruler of Portugal. Despite the nationalist’s success, John I of Castile won’t let the revolt go unanswered. In May 1384, a Castilian army crossed the Portuguese border and attacked Lisbon.

John I of Portugal
John of Aviz

Initially, the Castilian army expected to crush the Portuguese resistance easily. However, they soon realized that reality would be much different. Upon arriving in Lisbon, the Castilians found determined Portuguese defenders behind the capital’s strong walls. During the Castilian siege, John of Aviz demonstrated his leadership capabilities by commanding his troops. After an outbreak of plague in September, the Castilian army retreated from Portugal. Having achieved such an incredible victory, John became known as the Defender of the Realm amongst the Portuguese.

Birth of a New Dynasty

As Castilian forces withdrew from Portugal, John of Aviz’s support skyrocketed. Using his newfound influence, John called for a Cortes, an assembly of representatives from across Portugal, in April 1385 to decide the succession. Although Beatrice’s right to the throne was discussed, only a few representatives supported her claim. Instead, the overwhelming majority advocated for John to succeed Ferdinand. With the support of well-respected lawyer John das Regras, John’s claim was successful. On April 6, 1385, the newly crowned King John I established the Aviz dynasty as Portugal’s new ruler.

Despite John I claiming the throne, the Portuguese Interregnum wasn’t over. Recognizing that he needed more allies against Castile, the king sent ambassadors to England. After negotiating with King Richard II, the English king agreed to send military aid in May 1384. As part of the negotiations, each side pledged to support the other militarily when needed. Since Castile was still a threat to John’s throne, Richard followed through on his promise by sending English troops to assist the Portuguese.

The Battle of Aljubarrota

John I of Castile
John I of Castile

Angered at John I’s accession, John I of Castile began planning another invasion of Portugal. Initially sending an expedition force into Portugal, the Castilian soldiers would be defeated by John I of Portugal’s trusted constable, Nuno Alvares Periera. Supported by French troops sent by King Charles VI, the Castilian king led his 20,000 soldiers into Portugal. Intercepting the Castilian army, a smaller Portuguese force of 7,000 took up defensive positions on a ridge called Aljubarrota. On August 14, 1385, the Battle of Aljubarrota began.

Although the Portuguese-English army was vastly outnumbered, the well-rested army had time to set up strategically on the ridge to maximize their advantage. When the Castilian army finally showed up, the troops were exhausted from the long march to Lisbon. Understanding the situation, John I of Castile attempted to prevent an all-out assault. However, not everyone agreed. Fiery soldiers amongst the king’s ranks refused to wait and attacked the Portuguese instead.

Forced by his soldier’s rash actions, John I of Castile reluctantly ordered his army to advance. This strategic error played into the Portuguese’s hands. Capitalizing on the Castilian soldier’s recklessness, crossbowmen on the ridge mowed down waves of their enemy. The Portuguese strategy was so effective that the battle lasted barely an hour. Seeing the carnage, John I of Castile fled with the remains of his decimated army. John’s defeat at Aljubarrota was so devastating that the king could not muster another invasion of Portugal for years.


Portugal’s victory at the Battle of Aljubarrota effectively ended the Portuguese Interregnum. As a result of the battle, John I of Portugal secured his hold on the throne and ensured the survival of the Aviz dynasty. The king also strengthened his ties to England through the Treaty of Windsor in 1386 and by marrying a member of the English royal family, Philippa of Lancaster. The Aviz dynasty would rule Portugal for another 195 years until the death of King Henry in 1580.


Disney, A. R. (2009). A History of Portugal and the Portuguese Empire: From Beginnings to 1807 (Vol. 1). New York City, NY: Cambridge University Press.


Andy Tree

I'm a European history enthusiast who seeks to share his passion with others. I hope to inform and inspire readers with my posts!

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