Stonehenge

51.1789°N, 1.8262°W.

Megalithic ring on Salisbury Plain, Wiltshire, England. Construction occurred in stages from approximately 3000 BCE to 1500 BCE; the iconic sarsen ring and trilithon horseshoe were erected ~2500 BCE. The sarsen stones, sourced from Marlborough Downs 25 km to the north, weigh up to 25 tonnes each. The bluestones at the inner ring originated 240 km away in the Preseli Hills of southwestern Wales — the longest documented prehistoric stone transport in Europe. The principal axis of the ring aligns to the summer solstice sunrise and the winter solstice sunset along the same line. Recent ground-penetrating radar (Stonehenge Hidden Landscapes Project, 2010–14) has identified at least seventeen previously unknown ritual structures and over sixty buried stones within a 3 km radius.

The monument was already older than the pyramids when the Romans arrived, and they had no idea who built it.