Vast necropolis of the Neolithic and Bronze Age Boyne Valley culture in County Meath, Republic of Ireland. One of Europe's most remarkable prehistoric sites, the remains of four massive tumuli (burial mounds) containing passage-graves and burial chambers have been excavated at Newgrange, Knowth, and Dowth on the River Boyne between Slane and Drogheda, and at Fourknocks Hill, 20 km/32 mi to the southeast. The structures, dating from 3100 BC to 1800 BC, exhibit outstanding examples of megalithic abstract engraving and have yielded numerous Bronze Age and Early Christian artefacts. Their original purpose, as a centre of ritual or royal burial, is unclear but their precise alignment with the winter solstice suggests possible use as a calendar.
Newgrange, dating from 3100 BC, incorporates the world's oldest known astronomical observatory. Its tumulus, 80 m/278 ft in diameter and 9 m/30 ft high, is faced with sparkling white quartzite embossed with granite pebbles. The mound is bounded by 97 kerbstones and was once ringed by 38 monoliths, of which 12 remain. From the entrance, a 20 m/66 ft-long passage leads to a corbelled central chamber, 6 m/20 ft high; a narrow aperture allows the rising sun to enter only at the winter solstice. Three smaller recesses contain hollowed stones for cremated human bones and offerings. Geometric symbols decorate the kerbstones and other surfaces, including a unique triple spirals motif on the threshold stone.
Knowth has the greatest concentration of megalithic art in Europe, including lozenges, squares, sun symbols, triangles, zizags, and concentric arcs – also a feature of Breton sites. An unusual dotted pattern is similar to engraving found on Malta. The tumulus contains two extensive passage-graves, 34 m/118 ft and 40 m/140 ft in length, and is surrounded by 17 satellite tombs. Evidence of continuous occupation has been found from its construction around 3000–2500 BC until the 14th century.
Dowth tumulus encloses two passage-graves, but has suffered from Viking raids and pillaging for stones. The west passage opens into a cruciform chamber which contains a recess leading to a series of small compartments, a feature unique to the site.
Fourknocks Hill contains a huge passage-grave established 2200–1800 BC. Three niches in the burial chamber bear zizag motifs, and a human face is carved on one of the stones.