The greatest constitutional document of all time has gone on display at the Library of Congress. I don’t use that superlative lightly. The original copy of Magna Carta, on loan from Lincoln Cathedral, represents the most significant political moment in the history of our species. When its wax was sealed almost exactly 800 years ago, the law was, for the first time, elevated above the government.

We’re so used to that idea today that it takes a real effort of imagination to see how radical it must have been when it was first proposed. For thousands of years, the law had been whatever the biggest guy in the tribe said it was. The idea that an invisible, impalpable power stood above the king as surely as it stood above the poorest beggar, a power that was the property of the people as a whole, was utterly revolutionary.