Treaty of Windsor (1386)

{{Short description|Anglo-Portuguese diplomatic alliance}}

{{Use dmy dates|date=October 2019}}

{{For|other treaties called "Treaty of Windsor"|Treaty of Windsor (disambiguation){{!}}Treaty of Windsor}}

{{Infobox treaty

| name = Treaty of Windsor

| long_name = Treaty of peace, friendship and confederation between John I of Portugal and Richard II, King of England

| image = Treaty of Windsor.jpg

| image_width =

| image_alt =

| caption = Treaty of Windsor in the Portuguese National Archives

| type =

| context =

| date_drafted = 9 May 1386

| date_signed = 24 February 1387

| location_signed = Westminster

| date_sealed =

| date_effective =

| mediators =

| negotiators = * {{flagdeco|PRT|1385}} Fernando Afonso de Albuquerque

• {{flagdeco|PRT|1385}} Lourenço João Fogaça
• {{flagdeco|ENG}} Richard d'Alberbury
• {{flagdeco|ENG}} John Clanowe
• {{flagdeco|ENG}} Richard Ronhale

| original_signatories =

| signatories = * {{flag|Kingdom of England}}

• {{flag|Kingdom of Portugal|1385}}

| parties =

| ratifiers = * {{flagdeco|ENG}} Richard II of England

| depositor = Portuguese National Archives

| citations =

| language = Latin

| wikisource =

| wikisource1 =

}}

File:Anglo-Portuguese Treaty of Windsor, 9th May 1386.jpg

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.{{cite book |title=A History of Portugal |url=https://archive.org/details/in.ernet.dli.2015.152869 |first=H.V |last=Livermore |publisher=Cambridge University Press |year=1947 |page=179 |access-date=2021-10-07 |df=dmy-all }} 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. The Treaty of Windsor established a pact of mutual support.

Copies are preserved at the Torre do Tombo National Archive in Lisbon and The National Archives in London.{{cite web |title=History's Unparalleled Alliance: the Anglo-Portuguese Treaty of Windsor, 9th May 1386 |last=Trowbridge |first=Ben |url=https://history.blog.gov.uk/2016/05/09/historys-unparalleled-alliance-the-anglo-portuguese-treaty-of-windsor-9th-may-1386/ |website=history.blog.gov.uk |access-date=27 August 2024 |language=en |date=9 May 2016}}{{cite archive |item=Tratado de paz, amizade e confederação entre D. João I e Eduardo II, rei de Inglaterra, denominado Tratado de Windsor |item-url=https://digitarq.arquivos.pt/details?id=4186035 |item-id=PT/TT/GAV/18/3/25 |type=textual record |date=9 May 1386 |access-date=7 October 2021 |collection=Arquivo Nacional Torre do Tombo |institution=Direção-Geral do Livro, dos Arquivos e das Bibliotecas (DGLAB) |language=Portuguese}}

The historian Matthew Winslett says, "This treaty has been the cornerstone of both nations' relations with each other ever since."{{cite thesis |type=MA |last=Winslett |first=Matthew |others=Supervising Professor: Douglas Richmond |title=The Nadir of Alliance: The British Ultimatum of 1890 and Its Place in Anglo-Portuguese Relations, 1147–1945 |url=https://uta-ir.tdl.org/uta-ir/handle/10106/1093 |archive-url=https://rc.library.uta.edu/uta-ir/bitstream/handle/10106/1093/umi-uta-2206.pdf?sequence=1&isAllowed=y |archive-date=2008-09-17 |date=August 2008 |access-date=2021-10-07 |publisher=The University of Texas at Arlington |page=14 |quote= 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. |postscript=none}} Still in effect today, it is the longest-lasting diplomatic treaty in recorded history.BBC History Revealed magazine; May 2023 issue; p. 15