Silbury Hill is the tallest artificial mound in Europe - measuring around 40mn!
It consists of a ring of boulders, surmounted by alternating layers of chalk and clay, all the way to the top.
It would have taken 500 men around 15 years to build.
The land would have first had to be deforested, and the stones carved out and transported.
The chalk and clay along represent 250,000 cubic meters.
Nobody knows what it was for. There doesn't seem to be any other example of it anywhere else!