Scientists from Britain as well as teams from Austria, Germany, Norway and Sweden made the new discovery at the start of a new project to map the site.
They found a second henge-like structure - a circular area thought to have once held a wooden structure.
Professor Vince Gaffney of the University of Birmingham said Thursday the new find will completely change the way we think about the landscape around Stonehenge.
The origins of Stonehenge are unclear, but the ancient stone circle in southern England is one of the country's biggest tourist draws. The World Heritage site is particularly popular during the summer and winter solstices.