Centuries before the first massive sarsen stone was hauled into place at Stonehenge, the world’s most famous prehistoric monument may have begun life as a giant burial ground, according to a theory disclosed on Saturday.

More than 50,000 cremated bone fragments, of 63 individuals buried at Stonehenge, have been excavated and studied for the first time by a team led by archaeologist Professor Mike Parker Pearson, who has been working at the site and on nearby monuments for decades. He now believes the earliest burials long predate the monument in its current form....