The reign of King John was in all ways unlikely and, in most, dreadful. He was born in 1166 or 1167, the youngest of Henry II’s five sons, his ascension to the throne being, by the fingers on one hand, so implausible that he was not named after a king and, as a matter of history, suffers both the indignity of the possibility that he may have been named after his sister Joan and the certain fate of having proved so unredeemable a ruler that no king of England has ever taken his name. He was spiteful and he was weak, although, frankly, so were the medieval historians who chronicled his reign, which can make it hard to know quite how horrible it really was. In any case, the worst king of England is best remembered for an act of capitulation: in 1215, he pledged to his barons that he would obey “the law of the land” when he affixed his seal to a charter that came to be called Magna Carta. He then promptly asked the Pope to nullify the agreement; the Pope obliged. The King died not long afterward, of dysentery. “Hell itself is made fouler by the presence of John,” it was said. This year, Magna Carta is eight hundred years old, and King John is seven hundred and ninety-nine years dead. Few men have been less mourned, few legal documents more adored.

Magna Carta has been taken as foundational to the rule of law, chiefly because in it King John promised that he would stop throwing people into dungeons whenever he wished, a provision that lies behind what is now known as due process of law and is understood not as a promise made by a king but as a right possessed by the people. Due process is a bulwark against injustice, but it wasn’t put in place in 1215; it is a wall built stone by stone, defended, and attacked, year after year. Much of the rest of Magna Carta, weathered by time and for centuries forgotten, has long since crumbled, an abandoned castle, a romantic ruin.

Magna Carta is written in Latin. The King and the barons spoke French. “Par les denz Dieu!” the King liked to swear, invoking the teeth of God. The peasants, who were illiterate, spoke English. Most of the charter concerns feudal financial arrangements (socage, burgage, and scutage), obsolete measures and descriptions of land and of husbandry (wapentakes and wainages), and obscure instruments for the seizure and inheritance of estates (disseisin and mort d’ancestor). “Men who live outside the forest are not henceforth to come before our justices of the forest through the common summonses, unless they are in a plea,” one article begins.

Magna Carta’s importance has often been overstated, and its meaning distorted. “The significance of King John’s promise has been anything but constant,” U.S. Supreme Court Justice John Paul Stevens aptly wrote, in 1992. It also has a very different legacy in the United States than it does in the United Kingdom, where only four of its original sixty-some provisions are still on the books. In 2012, three New Hampshire Republicans introduced into the state legislature a bill that required that “all members of the general court proposing bills and resolutions addressing individual rights or liberties shall include a direct quote from the Magna Carta which sets forth the article from which the individual right or liberty is derived.” For American originalists, in particular, Magna Carta has a special lastingness. “It is with us every day,” Justice Antonin Scalia said in a speech at a Federalist Society gathering last fall.

Much has been written of the rule of law, less of the rule of history. Magna Carta, an agreement between the King and his barons, was also meant to bind the past to the present, though perhaps not in quite the way it’s turned out. That’s how history always turns out: not the way it was meant to. In preparation for its anniversary, Magna Carta acquired a Twitter username: @MagnaCarta800th. There are Magna Carta exhibits at the British Library, in London, at the National Archives, in Washington, and at other museums, too, where medieval manuscript Magna Cartas written in Latin are displayed behind thick glass, like tropical fish or crown jewels. There is also, of course, swag. Much of it makes a fetish of ink and parchment, the written word as relic. The gift shop at the British Library is selling Magna Carta T-shirts and tea towels, inkwells, quills, and King John pillows. The Library of Congress sells a Magna Carta mug; the National Archives Museum stocks a kids’ book called “The Magna Carta: Cornerstone of the Constitution.” Online, by God’s teeth, you can buy an “ORIGINAL 1215 Magna Carta British Library Baby Pacifier,” with the full Latin text, all thirty-five hundred or so words, on a silicone orthodontic nipple. ...