Treaty of Windsor (1386)

For other treaties called "Treaty of Windsor", see Treaty of Windsor.

The Treaty of Windsor is a diplomatic alliance signed between the Kingdom of Portugal and the Kingdom of England on 24 February 1387 in Windsor, Berkshire, and sealed by the marriage of King John I of Portugal (House of Aviz) to Philippa of Lancaster, daughter of John of Gaunt, 1st Duke of Lancaster.^[1] With the victory at the Battle of Aljubarrota, assisted by English archers, John I was recognised as the undisputed King of Portugal, putting an end to the interregnum of the 1383–1385 Crisis.^[1] The Treaty of Windsor established a pact of mutual support.^[1]

Treaty of Windsor

Treaty of peace, friendship and confederation between John I of Portugal and Richard II, King of England
Treaty of Windsor in the Portuguese National Archives
Drafted	9 May 1386
Signed	24 February 1387
Location	Westminster
Negotiators	Fernando Afonso de Albuquerque Lourenço João Fogaça Richard d'Alberbury John Clanowe Richard Ronhale
Signatories	Kingdom of England Kingdom of Portugal
Ratifiers	Richard II of England
Depositary	Portuguese National Archives
Language	Latin

Treaty in The National Archives, United Kingdom

Copies are preserved at the Torre do Tombo National Archive in Lisbon and The National Archives in London.^[2][3]

The historian Matthew Winslett says, "This treaty has been the cornerstone of both nations' relations with each other ever since."^[4] Still in effect today, it is the longest-lasting diplomatic treaty in recorded history.^[5]

See also

• Anglo-Portuguese Treaty of 1373
• British Ultimatum of 1890 – British diplomatic ultimatum to Portugal regarding Portugal's claims in AfricaPages displaying short descriptions of redirect targets
• Timeline of Portuguese history
• Anglo-Portuguese Alliance – 1386 alliance between the UK and Portugal
• Treaty of Tagilde – Anglo-Portuguese treaty signed in 1372
• Operation Alacrity