Now this is what I wish A Distant Mirror had been like. Danny Danziger and John Gillingham present a portrait of the times and events that helped shape the Magna Carta, which at the time I added 1215 to my collection and then actually started reading it had forgotten what that was. I'm certain my history teachers didn't forget to mention it, but then, the authors made several suggestions that they're writing to a primarily English audience, and so those readers were no doubt as aware of Magna Carta as I am, for instance, of Madison's Federalist Papers (though if you don't know what either are, don't assume they're literally comparable).
Basically, Magna Carta is the forerunner of democratic rule in the modern world. It was something King John was tricked into endorsing, even though he quickly backed out of it. King John was Richard the Lionheart's kid brother, and exactly the guy referenced in all those Robin Hood tales. He was a rat bastard who lucked into securing England's glorious future, and so is probably one of the world's great heroes. You can read all about him in the book, as well as everything that shaped his decisions as well as Magna Carta (literally the "big charter"). This is also the way that the Tecumseh biography I read earlier this year should have gone, but sometimes writers believe they have to smother a subject in order to cover it. I'll never understand that.
For good measure, the book includes the text of Magna Carta in the back, but that's another thing I didn't feel like reading. I do feel a little silly and ignorant now as opposed to when I started reading it, like I've regressed to an earlier age. But like many books I've been reading lately, there's some interrelatedness going on, with the added insight that people did in fact know that the world was round back then, and that it's only our assumptions about our ancestors that would lead us to believe otherwise. History is only history if we remember it. It can become something quite different, a comfortable fiction if you will, much as Magna Carta itself became. But you can't have everything.