BlockOut: Where exactly to you propose they acquired 1.3 tonnes of mercury? Where did it go when they were done with it? A 200 tonne megalith might be 2mx4mx5m, for a submerged surface area of roughly 38m³. 100 litres of mercury would make a wetted surface area of roughly 4 millimetres all around. What tolerances (roughly) on the channel walls would be required to support a 200 tonne block in only 100 litres of mercury? 1 millimetre? 2 millimetres? How much could they dig out at time, moving only enough to hold 100 litres of mercury? Say, 2 millimetres, front and back? How would they dig a gap, 4 metres wide, a metre deep but only 2 millimetres long? Just how strong must these canal walls be to sustain this pressire without deformity? Not clay. Rock. How long does it take 50 litres of mercury to creep 5 metres through a 4 millimetre gap from front to back? What rate of progress do you estimate they made from the trip from the quarry to the build site? And finally: have you done any of this analysis yourself? Why not?