Question: When was the 750th anniversary of the city in which the 2003 Priority Telecom Open was held?

Context paragraphs:
Seal of Mindaugas: The Seal of Mindaugas (Lithuanian: "Mindaugo antspaudas" ) is a medieval seal affixed to the October 1255 act by Mindaugas, King of Lithuania, granting Selonia to the Teutonic Knights.  An academic debate is ongoing to determine authenticity of the act and the seal as they might have been forged by the Knights.  If it is authentic then the seal is the only surviving contemporary depiction of Mindaugas.  As the most important surviving artifact from Mindaugas' times, the seal was a centerpiece of a special exhibition organized by the National Museum of Lithuania in 2003 to commemorate the 750th anniversary of Mindaugas' coronation.

Stedden: Stedden is a village in the borough of Winsen (Aller) in the Lower Saxon district of Celle in North Germany.  It lies on the river Aller and close to the river Örtze and has a population of just over 300.  In 1985 it celebrated its 750th anniversary.

2008 Dutch Open (tennis): The 2008 Dutch Open (also known as the "Priority Telecom Open" for sponsorship reasons) was a tennis tournament played on outdoor clay courts.  It was the 51st and last edition of the Dutch Open, and was part of the International Series of the 2008 ATP Tour.  It took place at the Sportlokaal de Bokkeduinen in Amersfoort, Netherlands, from 14 July through 20 July 2008.

Symphony No. 2 (Walton): The Symphony No. 2 by English composer William Walton was commissioned by the Royal Liverpool Philharmonic Society to celebrate the city's 750th anniversary in 1957.  The Royal Liverpool Philharmonic Orchestra conducted by John Pritchard gave the first performance on 2 September 1960 at the Edinburgh Festival.  George Szell gave the Continental Premiere with the Concertgebouw Orchestra in Amsterdam on 19 November 1960.  Szell also conducted the US Premiere of the work on 29 December 1960 with the Cleveland Orchestra in that city and a few months later they made its first recording.  Leopold Stokowski gave the work another early Continental performance in Vienna in May 1961 while on tour with the London Symphony Orchestra.

Svendborg: Svendborg (] ) is a town on the island of Funen in south-central Denmark, and the seat of Svendborg Municipality.  With a population of 26,672 (1 January 2014), Svendborg is Funen's second largest city.  In 2000 Svendborg was declared "Town of the year" in Denmark, and in 2003 it celebrated its 750th anniversary as a market town.  By road, Svendborg is located 195 km southwest of Copenhagen, 183 km south of Aarhus, 44.2 km south of Odense, and 28.5 km east of Faaborg.

2003 Priority Telecom Open: The 2003 Priority Telecom Open was a tennis tournament played on outdoor clay courts in Amersfoort, Netherlands and was part of the International Series of the 2003 ATP Tour.  It was the 44th edition of the tournament and was held from July 14 through July 20, 2003.

Amersfoort: Amersfoort ] is a municipality and the second largest city of the province of Utrecht in central Netherlands.  The city is growing quickly but has a well-preserved and protected medieval centre.  Amersfoort is one of the largest railway junctions in the country, because of its location on two of the Netherlands' main east-west and north-south rail lines.  It marked its 750th anniversary as a city in 2009.

Mindaugas Bridge: The Mindaugas Bridge is a bridge in Vilnius, Lithuania.  It crosses Neris River and connects Žirmūnai elderate with the Old Town of Vilnius.  The bridge was named after Mindaugas, King of Lithuania, and was opened in 2003 during the celebrations of the 750th anniversary of Mindaugas' coronation.  The bridge is 101 m in length and 19.7 m in width.

Tirnavia: Tirnavia is a mixed choir from Slovakia founded in 1988, on the occasion of the 750th anniversary of Trnava being granted free royal town privileges.  The choir was founded by Gabriel Kalapoš.  Following conductors were Andrej Rapant and Zuzana Holičková.  Current conductor is Michal Stahl.  Tirnavia's name is derived from the historical name of Trnava and Tirnavia confirms the rich tradition of choral singing in this town.  The choir members are mostly students of universities.

Sir William Boulton, 3rd Baronet: Sir William Whytehead Boulton, 3rd Baronet, {'1': ", '2': ", '3': ", '4': "} (21 June 1912 – 20 June 2010) was a prominent British barrister who served in the reconstruction of the German legal profession after the Second World War and then spent 25 years as Secretary of the Bar Council.  In this capacity he managed relations within the English legal profession and its relations internationally, as well as establishing the Senate of the Four Inns of Court that handles disciplinary action and organising the 750th anniversary of the signing of the Magna Carta and establishing a permanent memorial at the site.  He also wrote "Conduct and Etiquette at the Bar", which was the standard guide to the decisions of the General Council of the Bar for 25 years.

Supporting paragraphs: 2003 Priority Telecom Open Amersfoort
Answer: 2009