Treaty of Windsor (1386)

The Treaty of Windsor is the diplomatic alliance signed between Portugal and England on 9 May 1386 at Windsor 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 between the countries.[1]

Treaty of Windsor
Treaty of peace, friendship and confederation between John I of Portugal and Richard II, King of England
Treaty of Windsor.jpg
Treaty of Windsor
Drafted9 May 1386
Signed24 February 1387
DepositaryPortuguese National Archives

This document is preserved at the Portuguese National Archives.[2]

Historian Matthew Winslett says, "This treaty has been the cornerstone of both nations' relations with each other ever since."[3]

See alsoEdit


  1. ^ a b c Livermore, H.V (1947). A History of Portugal. Cambridge University Press. p. 179. Retrieved 7 October 2021.
  2. ^ "Tratado de paz, amizade e confederação entre D. João I e Eduardo II, rei de Inglaterra, denominado Tratado de Windsor" (9 May 1386) [textual record]. Arquivo Nacional Torre do Tombo, ID: PT/TT/GAV/18/3/25. Direção-Geral do Livro, dos Arquivos e das Bibliotecas (DGLAB). Retrieved 7 October 2021.
  3. ^ Winslett, Matthew (August 2008). The Nadir of Alliance: The British Ultimatum of 1890 and Its Place in Anglo-Portuguese Relations, 1147-1945 (PDF) (MA). Supervising Professor: Douglas Richmond. The University of Texas at Arlington. p. 14. Archived from the original on 17 September 2008. Retrieved 7 October 2021. This treaty has been the cornerstone of both nations’ relations with each other ever since. This is particularly true in regards to the Portuguese. The various treaties that follow it build upon the promises made at Windsor and never abrogate its terms, especially in the case of guarantees of territorial defense and military aid.