When I visited London a few years ago I went to the British Library and stumbled into their collection (and it was incredibly impressive). I had no idea they had two original Magna Cartas. If you have a chance to see the document at Harvard, you should! It's really something.
The Harvard document is a copy of Edward I's 1297 Great Charter that is still partly in force today.
There were earlier versions of the Magna Carta; originally authored by Stephen Langton, Archbishop of Canterbury in 1215, rejected, revised and eventually reissued and negotiated (largely by force) by William Marshal, 1st Earl of Pembroke in 1217.
