The Sarsen Circle and the horseshoe of trilithons were built in the third wave of construction, around 1650 BCE.
Stonehenge Inner Trilithons
This inner group of trilithons is part of ten upright stones that form a horseshoe and were erected within the larger Sarsen Circle. You will no longer be able to duplicate this picture. In 1989 the site was roped off to protect it from the vandals who were climbing the stones and taking souvenirs.