Silbury Hill, the English Giza, is a 37-metre high pile of gravel, sarsen stone, chalk, rubble and earth that was developed by many people over many hundreds of years (from about 2400BC) for some unknown reason or reasons. It is supposedly the largest pre-historic construction in Europe.
In their recent study, The Story of Silbury Hill, Leary and Field note how modern attempts to put the hill into context have been focussed on the monetary value required to build it anew:
"John Aubrey claimed it would cost 'four score thousand pounds to make the hill now'. William Stukeley put it at the lower cost of £20,000 in 1743, while Edward Drax corrected him, suggesting that it would cost exactly £56,495 and 9d."
Leary and Field rightly point out that approaching Silbury Hill as though it were an engineering project implies a failure of imagination and a misunderstanding of the history of accumulating earth.