Ireland is an island in the North Atlantic separated from Great Britain by the North Channel. Dublin is the capital and largest city of Ireland, founded as a Viking settlement and later becoming the capital of the Kingdom of Dublin. Dublin has many landmarks and monuments dating back hundreds of years, including Dublin Castle founded in 1204 as a major defensive work, as well as newer monuments like the Spire of Dublin. Irish culture traditionally divided north and south along the River Liffey, and popular sports in Ireland include hockey, golf, and Irish football. St. Patrick's Day is celebrated each March 17th to honor St. Patrick, with celebrations lasting 5 days and people wearing shamrocks or green clothing.