Location: Salisbury Plain, Wiltshire, England Date constructed: c. 3100 BC - 2000 BC Designers/Builders: Unknown Function: Possibly astronomical computation or Religious/ritual site

To see Stonehenge, silent and solitary on the heights of Salisbury Plain is to be immediately aware of its mysterious power and brooding presence. Why is it there? What is it for? Who constructed it? How did they do it, armed only with brute strength and the most primitive tools? The builders left no written records so we can only make educated guesses, based on research and archaeology.

Stonehenge itself dates from around 3100 BC - although traces of post holes dating to 8000 BC have been found near the site. It was constructed in three phases.

The first phase, built around 3100 BC comprised a ditch, a bank and the Aubrey Holes - round pits roughly one metre wide and one metre deep. Archaeological excavations have found human remains in the chalk filling, but these seem to have been part of a religious ceremony, rather than graves. After this the site was abandoned for over 1,000 years.

The second phase started about 2150 BC and involved the famous bluestones which originated in the Preseli Mountain in South West Wales, some 200+ miles away. The builders would have had to drag the stones on sledges and rollers by sea, river and overland to the site. Some think the stones might have been carried by glacial action to Somerset. At Stonehenge the stones were erected in the centre of the site to form an incomplete double circle.

In 2000 BC the third phase began with the arrival of the massive Sarsen stones, weighing up to 50 tons. These were dragged overland from the Marlborough Downs over 20 miles away. The stones were planted in an outer circle, topped with huge stone lintels. Five trilithons were erected in a horseshoe pattern inside the outer circle.

Over the next few hundred years further changes were made, particularly the rearrangement of the bluestones into a horseshoe shape, leading to the pattern of stones that we know today.

What was the purpose of this massive structure? Again, we don't know for sure. Theories range from a pre-historic Lourdes, to an astronomical computational tool or a ritual/religious site. Whatever its purpose, it is one of our most impressive landscape treasures.