Slane Castle sits on the north bank of the Boyne, eight miles upstream of Drogheda, in a parkland landscaped by Capability Brown. The ground south of the castle slopes down toward the river in a near-perfect concave sweep - a natural arena that can hold 80,000 people facing one stage at the bottom, with the castle looking down behind them. There is no other site quite like it for outdoor music. Rain rolls off the surrounding hills toward the Boyne. The acoustics, helped by the bowl shape, are unusually clean. And because the site is essentially a private estate, the Conyngham family who own it have always controlled how often the festival happens. Some years there is one. Some years two. Some years - 2008, 2010, 2012, 2014 - none at all, because no act caught Lord Henry's imagination.

Seven concerts in seven years. Thin Lizzy in 1981. The Rolling Stones in 1982. U2 in 1983 - although the castle was refused permission that year and the concert moved to Phoenix Park Racecourse in Dublin, the only time Slane has been held off-site. Bob Dylan in 1984, with Bono guesting on the encore - the first time the Slane stage saw a U2 member after their 1983 set. Bruce Springsteen in 1985 - his Irish debut, three hours with no support, 100,000 people. While he sang The River, video screens showed footage of the actual River Boyne flowing past the field. Springsteen kept the footage for the rest of the tour. Queen in 1986, four years before Freddie Mercury died. David Bowie in 1987, on the Glass Spider tour, his last visit to Ireland in his lifetime. Seven concerts, seven of the biggest acts on Earth. It cemented Slane's reputation.

U2 have headlined Slane more times than anyone else, and twice in the same year - 25 August and 1 September 2001 - because tickets for the first show sold out in 45 minutes and the Taoiseach asked the Minister for the Environment to fast-track legislation to allow a second one. The second concert coincided with Ireland's World Cup qualifier against the Netherlands, and at the request of fans, the match was shown on stage screens between Nelly Furtado and Ash. U2 came on after Ireland drew. The second show was filmed for the live video U2 Go Home, and it is now considered one of the band's definitive concert documents - Bono speaking onstage about his father Bob Hewson, who had died of cancer ten days earlier. U2 had played their first Slane in 1981 as openers for Thin Lizzy. They returned in 1983 as headliners. The 2001 shows brought them home as the biggest band in the world.

Across forty years, the headline list reads like a museum of rock. Bryan Adams in 2000. Red Hot Chili Peppers in 2003 - their first Slane was 2001 as support; they came back top-billed two years later. Madonna in 2004, when one Irish manager said the crowd treated her like a football match. The Rolling Stones returned in 2007, by then the only other act besides U2 to have headlined Slane in two different decades. Oasis headlined 2009 - they had played 1995 as support for Robbie Williams's headline set. Kings of Leon in 2011 announced their longest-ever show. Bon Jovi headlined 2013, then Eminem played a second show that summer to 80,000 people; he had infamously cancelled his 2005 Slane date after entering rehab, and the promoter had to seek damages in the High Court. Foo Fighters 2015. Guns N' Roses 2017. Metallica 2019. Harry Styles in June 2023. Each one walks out to find the green bowl already full, the river behind them, the castle floodlit above.

The minimum age of entry was 18 for Slane's first 25 years. In 2006 it was reduced to 16 after complaints. Even with that, generations of Irish teenagers have travelled to Slane as a rite of passage - the long bus from Dublin, the walk down the hill from the village, the queue along the perimeter fence, the first sight of the stage at the bottom of the field. The Conyngham family treat it as their event. Henry Conyngham, the 8th Marquess - known until 2009 as the Earl of Mount Charles - has personally booked or vetoed every headline act since 1981. The castle stays open as accommodation; some of the bands sleep upstairs. The site cleans up over weeks. Then the cattle return to the field, and the place is a private estate again until the next August.