

Here is some information I found online:
Archaeologists believe the standing stones were erected around 2200BC, and the surrounding circular earth bank and ditch have been dated to around 3100BC. It is thought to have evolved from a simple bank and ditch in the Neolithic period and is characterised by wooden materials. The very sophisticated stone circle was built on the axis of the midsummer sunrise and rearranged several times during the Bronze Age. As with most mysterious and historic sites, Stonehenge is considered sacred.
The site is the subject of many myths and legends and no one really knows how or why it was built, though there are many theories. The engineering feat is still bewildering. It pre-dates the Egyptian, Mycenean, eastern Mediterranean and druid influences, so was probably conceived and built by Britain's own indigenous people. (http://getaway.ninemsn.com.au/article.aspx?id=602896)
Here are several more photos: