Question: The Robbie Williams album "Live at Knebworth" is a compilation of songs performed during shows at a festival that began in what year?

Context paragraphs:
Robbie Williams: Live at the O2: Robbie Williams: Live at the O2 is a live album released by British singer-songwriter Robbie Williams on 24 November 2012, as a commemoration of his live performances at The O2, London on 22, 23 and 24 November 2012.  The album was available to attendants of the concerts straight after the performances, and later via Williams' official website.  The album features guest appearances from Gary Barlow and Guy Chambers.  The album contains three discs, each of which contains part of the specific concert in question.

Concerts at Knebworth House: The Knebworth Festival is a recurring open air rock and pop concert held on the grounds of the Knebworth House in Knebworth, England.  The festival first occurred in 1974 when The Allman Brothers Band, The Doobie Brothers and other artists attracted 60,000 people.

Close My Eyes (Sander van Doorn song): "Close My Eyes" is an electronic song from Dutch techno and trance music DJ and producer Sander van Doorn.  The song features Robbie Williams and production by Pet Shop Boys and Chris Zippel.  The remix is of the original version of the song called "We're the Pet Shop Boys", a track recorded by Robbie Williams, featuring Pet Shop Boys, from his album "Rudebox".  The track peaked at number five on the U.S. "Billboard" Hot Dance Club Songs chart.  An official music video exists.

The Robbie Williams Show: The Robbie Williams Show is a live DVD and VHS video by Robbie Williams, recorded in 2002 in Pinewood Studios before the release of the album "Escapology".  Many of the album's songs were performed for the first time here, with Robbie jokingly declaring to some fans that they may have already heard some of the new songs (such as "Something Beautiful"), but only through unauthorized Internet leaks.

Ancora: Ancora is the second studio album released by classical crossover vocal group Il Divo.  The album was released in the United Kingdom and other parts of Europe on 7 November 2005, excluding the United States and Latin America.  The album was later released in the United States and Latin America on 24 January 2006.  It debuted at number one on the "Billboard" 200 on the week of releases.  The album contains one song partially in Latin, one song performed in Italian, two songs performed in French, two songs performed in English, and six songs performed in Spanish, excluding the bonus track.  The album features the single "I Believe in You", performed with Céline Dion, that is also featured on her international album, "On Ne Change Pas".

What We Did Last Summer: What We Did Last Summer – Robbie Williams: Live at Knebworth is a live DVD by Robbie Williams, recorded between 1–3 August 2003 at Knebworth, England as part of the Weekends of Mass Distraction Tour, the second last venue on the first leg of the tour.

Live at Knebworth: Live at Knebworth, also known as Live Summer 2003 with different cover text, is a live album by English pop singer Robbie Williams, recorded and released in 2003.  The album is his first live album, and is a compilation of songs performed during three consecutive shows at Knebworth, England on 1–3 August 2003.

Live at the Albert: ""Robbie Williams: Live at the Albert"" is a DVD that was released in December 2001 of the show performed on 10 October 2001; concert that Robbie Williams gave at Royal Albert Hall a month before the release of the album Swing When You're Winning.  It has since been certified 6x Platinum in the United Kingdom and 2x Platinum in Germany.

Il Divo (album): Il Divo is the self-titled debut studio album to be released by classical crossover vocal group Il Divo, formed by Simon Cowell in 2004.  The album was released on 1 November 2004 in the United Kingdom, via Syco Music, and on 19 April 2005 in the United States, via Columbia Records.  The album contains three songs performed in English, six songs performed in Italian, and three songs performed in Spanish, excluding the bonus track.  As of December 2013, the album had sold more than 1.5 million copies in the UK.  The album has sold more than 5,000,000 worldwide copies to date.

Make Me Pure: "Make Me Pure" is a song by British pop singer Robbie Williams, released as the second single from his album "Intensive Care" in late 2005.  It was written by Robbie Williams, Stephen Duffy, and Chris Heath.  It was first released in New Zealand and Australia as a promotional single intended to advertise the album.  A video was shot with Williams performing in a garage, however, its performance was poor with focus on Williams' debut single "Tripping" from that album.  It was featured on physical copies of the single "Tripping".  A physical CD single was released exclusively in Mexico.

Supporting paragraphs: Live at Knebworth Concerts at Knebworth House
Answer: 1974