Geoffrey of Monmouth, writing in the 12th century, believed that the stones were used for healing and had been brought from Africa to Ireland by giants and then Merlin brought them to Britain.
In the middle of the 17th century a survey of the stones was conducted by John Aubrey who concluded that the stones were the work of Druids. He demonstrated that the stones had some sort of role in astrology or were used as a calendar.
In 1655 the architect John Webb argued that Stonehenge was in fact a Roman temple.
The scientist Joseph Lockyer suggested that it was a giant astronomical observatory in 1906.
Another astronomer, Gerald Hawkins, suggested in 1966 that the stones were a prehistoric computer used to make complex calculations of planetary alignments.
J.F.S. Stone believed the stones may have been erected to cement an alliance or to celebrate a victory over a conquered enemy.
Some people claim to have seen UFOs in the vicinity of Stonehenge which has lead to a minority believing the stones to be an alien landing site.
In recent times many archaeologists have come to believe that the stones were part of a ritual relating to the funerals or a cult of the dead, based on the numerous burial sites around Stonehenge.
Dr. Anthony M. Perks, a retired gynecologist, proposed a theory that the henges resemble the human vulva and that Stonehenge was a place of life and birth instead of death.
