This is Silbury Hill, a huge Neolithic monument in Wiltshire, England. Its age is estimated at 4,400 years but archaeologists still don't know what it was for. They have reached the core of the hill where they've found blades of grass which are still green and sarcen stones of the same stone as nearby Avebury and Stonehenge which were carefully placed at every stage of the building. They didn't find a burial chamber of a Celtic King or any treasure.
The bottom layer was gravel, covered by three larger mounds of chalk boulders and chalk rubble. It was, at 40 metres high, the largest artificial hill in Europe. This was in an age when survival was day to day so I can't imagine why they would take the time and effort to create this.
Jim Leary, an English Heritage archaeologist, said the original builders left the site without any man made rubbish except for the antler picks used in the building. Dating of one of the antlers proved the structure was complete almost 1,000 years before the last arrangement of the stones at Stonehenge. The top came later, carved flat to take a Saxon or Norman building.
The once sacred monument will now be cleared of modern activity and exploration tunnels sealed.
Some believe that Silbury was built to represent the mother goddess, with the mound symbolising the pregnant womb, the writer Michael Dames has identified Silbury Hill as the winter goddess and Moses B. Cotworth stated that Silbury may have been used as a giant 'sundial' to determine seasons and the true length of the year.
It could be that it provided a means of following solar activity, as shadows were cast from its summit. Silbury is also at the centre of alignments for straight prehistoric tracks which the Romans bricked over and there's evidence of ancient Ley lines (energy grids) linking key sites in the area.
Near Silbury there was another mystery. On the 2nd and 3rd of August 2004, the Mayan Calender crop circle, voted one of the best ever made, appeared. Made by aliens, electro magnetice floating orbs or men with rope and boards, it still looks fantastic until you remember it was made in two stages not in one night.
There are two good sites for crop circles http://www.lucypringle.co.uk/ Lucy Pringle explores and explains crop circles and their effects on visitors. This site has a stunning collection of photographs of the crop circles.
http://www.circlemakers.org/ is the site of England's crop circle makers, the rope and board men but even they don't claim all circles as their own.
Civilizations rise and fall but mysteries go on forever.