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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 recognized 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
Signed1386 (1386)

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 1947, p. 179.
  2. ^ "Tratado de paz, amizade e confederação entre D. João I e Eduardo II, rei de Inglaterra, denominado Tratado de Windsor" (in Portuguese). Portuguese National Archives Digital Collection. Retrieved 4 January 2013.
  3. ^ Winslett 2008, p. 3.