One of Irelands most famous Neolithic passage graves, Knowth is in the valley of the Boyne River, at the ancient monument of Brú na Bóinne nearby famous Newgrange. This monument was built after Newgrange, roughly 5,000 B.C.E. (Before the Common Era). It is believed to have been built before Dowth. It is similiar in size to Newgrange, but is surrounded by 18 satellite mounds. The ‘Great Mound’ has two passages with entrances in the opposite sides – passage on the west is 34 meters long, passage on the east is 40 meters long, both ending at a cruciform chamber with a corbelled roof. Mythologically believed to be a Faerie mound – A Sidhe – Archaeologists catalogue the site as a passage grave based on three recesses and basin stones found within the chambers into which the cremated remains of the dead were placed. The monument also has astronomical features. Tied in with Dowth and Newgrange, the area has been designated as a World Heritage Site by UNESCO in 1993. The only access to the site is via guided tour from the Bru na Boinne Visitor Center that take place from April thru October. Excavations begun at Knowth in 1962, and in 1967 the discovery of the first passage and chamber were accomplished. Later excavations revealed the second passage and chamber, as well as a collection of rock art and decorated stones that amount to a quarter of Western European Neolithic Rock Art. Excavations revealed pottery, flint, houses, and other artifacts that determined Neolithic settlement around 4,000 B.C.E. Rock formations and art signify calendars, sundials, calendar stones, and stones to calculate the lengths of the lunar tropical month – ‘synodic’ and the length of the year in the Lunar Stone. The Calendar Stone seems to track the ‘Metonic Cycle’ of the Moon. The Main Mound has 124 existing Kerbstones forming the Kerb that at its base that are circular and measuring 80 meters east-west by 95 meters (north-south). Most of the Kerbstones forming this Kerb are oblong and average 2.5 meters in length. This is the largest of all passage graves in the area. There are over 200 decorated stones found here containing a wide variety of images from crescents, spirals, lozenges, and serpentiforms that have been carved on the stones with some ‘hidden art’ on the backs of the stones. There is also evidence for late Neolithic and Bronze Age activity, most of which is based from the existence of grooved ware timber circles located near the entrance of the eastern passage. Evidence for rituals here consists of a large number of votive offerings found in and around the area of the timbers. Knowth was used by the Normans in the 12th century. The site was also used briefly as a burial site with over 35 cist graves found on site that appear to be Celtic burials. Many of the bodies buried here were female. Two young men were buried – decapitated and buried together with a gaming set. During Christian occupation, the hill became a fort with encircling ditches and souterrains added converting the site into a habitation site. The monument fell into the hands of the monks of the Mellifont Abbey nearby. The mound was then later used as a grange or farm with stone walls construced atop and stone buildings within those walls. When the monasteries were dissolved the site was taken over by the state in 1939.