MY ONLY GRUMBLE about Over the Edge of the World is the title, with its superior, twenty-first-century nod towards the image of a boatload of wide-eyed innocents sailing terror-stricken towards expected destruction as they tumble off the flat world and into the void. That is a modern myth: it had been well known since at least the time of Pythagoras of Samos in the sixth century BC that the earth was a globe.

No one pretends that Magellan's flotilla was crewed by Greek philosophers, but there has never been any evidence for the frequently repeated assertion that the ordinary people of the Middle Ages and beyond believed the earth was flat. On the contrary, some recent research suggests that it was not until