4th-millennium BC architecture

Stonehenge is a prehistoric megalithic structure on Salisbury Plain in Wiltshire, England, west of Amesbury. It consists of an outer ring of vertical sarsen standing stones, each around high, wide, and weighing around 25 tons, topped by connecting horizontal lintel stones which are held in place with mortise and tenon joints—a feature unique among contemporary monuments. Inside is a ring of smaller bluestones. Inside, these are free-standing trilithons, two bulkier vertical sarsens joined by a single lintel. The whole monument, now in ruins, is aligned towards the sunrise on the summer solstic

thumb|Poulnabrone dolmen, [[the Burren, County Clare, Ireland]] thumb|Dolmens in Amudalavalasa|Amadalavalasa, [[Andhra Pradesh, India]]