Often the bottom of the stones are rounded so the process of righting them, in the hole, is made easier. Have a look at Harold's Stones. How far, and in what direction, stones have slipped in three and a half thousand years is another question. Vertical stones look dull (in my experience). Defy gravity and create tension - but where does that leave Stonehenge ?

'Give me a lever and I'll move the world' - attributed to Ron Knee, in 1948, talking about the Neasden Wanderers.