Newgrange

Calibrated C14 dating: construction around 3200 BC (O'Kelly 1982; Lynch et al. 2014, Antiquity), i.e. ~600 years before the pyramids of Giza and ~1,000 years before Stonehenge.

Solstice alignment: on 21 December, a beam of light travels 19 m through the roof-box and illuminates the chamber for exactly ~17 min — an alignment rediscovered by M.J. O'Kelly on 21 December 1967 (O'Kelly 1982, Thames & Hudson).

Architecture: a 19 m passage of orthostats, a cruciform chamber, a corbelled vault 6 m high, watertight for 5,000 years without mortar or cement; water-drainage grooves carved into the roof slabs (O'Kelly 1982).

Ancient DNA (Cassidy et al. 2020, Nature 582, 384–388, DOI 10.1038/s41586-020-2378-6): individual NG10, found in the main niche, is the offspring of a first-degree incestuous union; a distant-kinship network was identified across 44 Irish genomes spanning ~2,100 years.

Megalithic art: 97 kerbstones engraved with spirals, lozenges and concentric circles before being set in place; the triple spiral in the rear chamber predates the arrival of the Celts by 2,500 years (O'Kelly 1982).

Genetic context: around 3800 BC, Ireland is colonized by descendants of Anatolian farmers via the Iberian Peninsula and the Atlantic coast, supplanting the Mesolithic hunter-gatherers (Cassidy et al. 2020).

Site listed as UNESCO World Heritage in 1993 (Brú na Bóinne complex); white quartzite and granite façade reconstructed by O'Kelly in the 1970s from stones found collapsed in front of the entrance.