In 2013, as grounds dried up on the monument site, several particularly brown, scorched spots of grass began to appear where one might expect stones to lie if Stonehenge's partial circle was completed. The groundskeeper called the spots to the attention of local archaeologists.
"I was standing on the public path looking at the grass near the stones and thinking that we needed to find a longer hosepipe to get the parched patches to green up," Tim Daw told BBC News. "A sudden lightbulb moment in my head, and I remembered that the marks were where archaeologists had looked without success for signs that there had been stone holes, and that parch marks can signify them."
Experts believe that Stonehenge was likely constructed in several stages during the Neolithic period, its beginning and completion spanning a few hundred years sometime between 3000 BCE to 2000 BCE.
Archaeologists have cautiously confirmed Daw's suspicions; though they say the brief period of time limited their ability to arrive at a more affirmative conclusion. Future droughts, however, could allow for scientists to carry out further examinations.
"Ideally the survey would have differentiated between marks caused by parching -- the majority -- and those caused by lusher growth," scientists wrote in a paper published this week in the journal Antiquity. "It would have also have graded the marks into 'definitive', 'probable' and 'possible' categories," the study's authors continued. "This was not possible, and the result must therefore be treated with caution."
"If these stone holes actually held upright stones then we've got a complete circle," Susan Greaney -- historian with the Stonehenge care-taking and cultural preservation group English Heritage -- told the BBC. "It's really significant, and it shows us just how much we still have to learn about Stonehenge."