The Stonehenge Hidden Landscapes Project team has discovered evidence for a row of up to 90 standing stones, some of which may have originally measured up to 4.5 meters in height. Many of these stones have survived because they were pushed over and the massive bank of the later henge raised over the recumbent stones or the pits in which they stood. Hidden for millennia, only the use of cutting edge technologies has allowed archaeologists to reveal their presence without the need for excavation.
http://www.sciencedaily.com/releases/2015/09/150907114556.htm