One way to find out what’s under a rock is to lift it up and look. That’s impossible when the rock is Stonehenge, the ancient stone circle in Wiltshire, England. Fortunately, archeologists have found a new way to look underneath Stonehenge and discovered it may not be the only Neolithic monument on the spot.

The Stonehenge Hidden Landscapes Project is a four-year collaboration between the University of Birmingham and the Ludwig Boltzmann Institute for Archaeological Prospection and Virtual Archaeology in Austria. Its researchers used ground-penetrating radar and 3D laser scanning to create a detailed subsurface map of about four square miles surrounding Stonehenge. What they found is what appears to be 15 previously unknown late Neolithic monuments along with other henges, barrows (burial mounds), pits and ditches.

One of the most interesting discoveries is a trough that bisects the “Cursus,” a 2-mile east-west ditch. While the purpose of the Cursus is unknown, archaeologist Vince Gaffney of the University of Birmingham believes the trough may have been an entrance for people to use when ceremonially approaching Stonehenge from the north. Gaffney says this and the other discoveries suggest the area around Stonehenge was not isolated but instead filled with human activity.

A large pit discovered at the east end of the Curcus aligns with Stonehenge and a previously found pit at the west to form a triangle that marks sunrise and sunset on the summer solstice. Gaffney thinks the pits were used for fires to help mark these lines of sight at night.

These new findings by The Stonehenge Hidden Landscapes Project will be presented on September 9 during a press conference at the British Science Festival 2014 in Birmingham, England.

The maps will be for further historical research and to conduct new searches while giving future excavators better accuracy while minimizing any disturbance to Stonehenge.