96. How much did Hadrian’s Wall weigh?

This is a fairly meaningless question, except as an indication of how much material the Roman army would have had to acquire, move, and assemble. Assuming a volume of 10m³ for a metre of curtain wall (including parapet and consisting of dressed sandstone facing, rubble core, and lime mortar), and a mass of 20 tonnes for the requisite amount of stone and mortar, the curtain wall alone would have weighed in the order of 2.4 million tonnes over its 119km. With turrets, milecastles, and forts added in, this would probably come closer to 3 million tonnes.

Further reading: Hill 2006