Northwest of Newgrange, the burial mound of Knowth was built around the same time. It has the greatest collection of passage-grave art ever uncovered in Western Europe, and has been under intermittent excavation since 1962 (you may see archaeologists at work when you visit).
Early excavations soon cleared a passage leading to the central chamber which, at 34m, is much longer than the one at Newgrange. In 1968 a 40m passage was unearthed on the opposite side of the mound.
Also in the mound are the remains of six early-Christian souterrains (underground chambers) built into the side. Some 300 carved slabs and 17 satellite graves surround the main mound.
Human activity at Knowth continued for thousands of years after its construction, which accounts for the site's complexity. The Beaker folk, so called because they buried their dead with drinking vessels, occupied the site in the Early Bronze Age (c 1800 BC), as did the Celts in the Iron Age (c 500 BC). Remnants of bronze and iron workings from these periods have been discovered. Around AD 800 to 900, it was turned into a ráth (earthen ring fort), a stronghold of the very powerful O'Neill clan. In 965 it was the seat of Cormac MacMaelmithic, later Ireland's high king for nine years, and in the 12th century the Normans built a motte and bailey (a raised mound with a walled keep) here. The site was finally abandoned around 1400.