Archaeologists have discovered evidence of what they believe was a second Stonehenge located a little more than a mile away from the world-famous prehistoric monument.

The new find on the west bank of the river Avon has been called "Bluestonehenge", after the colour of the 25 Welsh stones of (A) ________.

Excavations at the site have suggested there was once a stone circle 10 metres in diameter and surrounded by a henge – a ditch with an external bank, according to the project director, Professor Mike Parker Pearson, of the University of Sheffield. The stones at the site were removed thousands of years ago but the sizes of the holes in (B) ________ indicate that this was a circle of bluestones, brought from the Preseli mountains of Wales, 150 miles away.

The standing stones marked the end of the avenue (C) ________, a 1¾-mile long processional route constructed at the end of the Stone Age. The outer henge around the stones was built about 2400BC but arrowheads found in the stone circle indicate the stones were put up as much as 500 years earlier.

Parker Pearson said his team was waiting for results of radiocarbon dating (D) ________ whether stones currently in the inner circle of Stonehenge were originally located at the other riverside construction.

Pearson said: "The big, big question is when these stones were erected and when they were removed – and when we get the dating evidence we can answer both those questions."

He added: "We speculated in the past (E) ________ at the end of the avenue near the river. But we were completely unprepared to discover that there was an entire stone circle. Another team member, Professor Julian Thomas, said the discovery indicated (F) ________ was central to the religious lives of the people who built Stonehenge. "Old theories about Stonehenge that do not explain the evident significance of the river will have to be rethought," he said. Dr Josh Pollard, project co-director from the University of Bristol, described the discovery as "incredible".