Under excavation since 1962, the prehistoric site of Knowth is comparable in size and shape to Newgrange, standing at 40 feet and having a diameter of approximately 214 feet. Some 150 giant stones, many of them beautifully decorated, surrounded the mound. More than 1,600 boulders, each weighing from one to several tons, were used in the construction. The earliest tombs and carved stones date from the Stone Age (3000 BC), and in the early Christian era (4th–8th century
AD) it was the seat of the High Kings of Ireland. Much of the site is still under excavation, and you can often watch archaeologists at work. Tours of the site depart from the Brú na Bóinne Visitor Centre.