Who Built Stonehenge?

Stonehenge, located on the Salisbury Plain in Southern England, has long been associated with Druids, a group of wise men present in England more than 2000 years ago. Still today at Summer Solstice, the longest day of the year, Druid celebrations are held at Stonehenge. But were they the actual designers? Excavations underneath the stones have revealed artifacts, like antler horns, carbon dated at 4000 years ago. Bodies found buried nearby are of the same age. This rules out the Druids, as well as the Romans who followed them. This even pre-dates immigrant settlers from Europe. That leaves a primitive people known as the Ancient Britons, who lived at the start of the bronze age.

Great precision was used in assembling the 15,000 tons of rock into circles. Did they have the know-how?