There is a field in Surrey, flat and a little soggy, where the Thames loops lazily past on its way to London. On most days nothing happens there at all. Yet in June 1215 that unremarkable meadow — Runnymede — became the stage for one of the most consequential arguments in English history. A king who believed he answered to no one was forced, at swordpoint really, to admit that even he stood beneath the law. We call the document that came out of it Magna Carta, the Great Charter, and people have been quarrelling over what it means ever since.

To understand why it happened, you have to meet King John, and almost nobody who met King John came away impressed. He was the youngest son of Henry II, never meant to rule, and he got the throne in 1199 only because his glamorous brother Richard the Lionheart died with no children. John was clever — genuinely clever — but also suspicious, grasping and spectacularly unlucky. He lost Normandy and most of the family’s French lands to the king of France, a humiliation that earned him the mocking nickname “Softsword.” And losing wars is expensive.

To claw back what he’d lost, John squeezed his barons for money in every way he could imagine. He raised the feudal taxes, sold royal favours, charged outrageous fees for inheritances, and seized estates on flimsy pretexts. He even fell into a furious row with the Pope over who should be Archbishop of Canterbury, and got the whole of England placed under a papal interdict for years — no church services, no marriages, no proper burials. By the time he patched things up with Rome, his own nobles had simply had enough.

In the spring of 1215 a group of northern barons renounced their loyalty and took up arms. This was no peasant grievance; these were the wealthiest and most powerful men in the kingdom, and crucially they captured London. With his capital gone and his support crumbling, John had no real choice but to negotiate. The two sides met at Runnymede, deliberately chosen as neutral ground between the royal castle at Windsor and the rebel base at Staines.

What they produced was, at first glance, a rather technical list. Many of its sixty-odd clauses deal with the specific complaints of feudal lords — inheritance fees, the treatment of widows, the king’s forests, fish-weirs on the rivers. If that were all Magna Carta contained, it would be a footnote. But buried among the bookkeeping were a handful of clauses that reached for something larger, and those are the ones the world remembers.

One promised that no free man could be imprisoned, stripped of his rights, exiled or destroyed except by the lawful judgement of his equals or by the law of the land. Another promised that justice would not be sold, denied or delayed. The language was medieval and the intended beneficiaries were a narrow slice of society, but the principle underneath was radical: the king’s will was not the same thing as the law, and there were limits even he could not cross.

Here is the part schoolbooks tend to skip. Magna Carta failed almost immediately. John had no intention of keeping his word, and within weeks he had written to the Pope, who obligingly declared the whole charter null and void. England tumbled straight into civil war. John then did everyone a favour, historically speaking, by dying of dysentery in 1216, leaving the throne to his nine-year-old son. The boy-king’s advisers, desperate for support, reissued Magna Carta — without the most radical clauses — as a peace offering. And so the document that had been dead on arrival was quietly resurrected, revised and reissued again and again over the following decades until it slipped into the permanent fabric of English law.

That slow afterlife is what really matters. Centuries later, lawyers and rebels reached back to Magna Carta whenever a ruler overreached. Seventeenth-century parliamentarians waved it at the Stuart kings. American colonists invoked it against George III, and you can hear its echo in their talk of due process and trial by jury. Much of this was, strictly speaking, a creative misreading — the barons at Runnymede were not dreaming of democracy or universal rights. But ideas have a way of outgrowing the people who first scribble them down.

So the importance of Magna Carta lies less in what it actually said in 1215 than in what later generations decided it meant. It planted a stubborn idea in the English imagination: that power must answer to something beyond itself. In the next instalment we’ll turn from grand constitutional drama to something far more frightening and far more democratic in its cruelty — the arrival, in 1348, of the Black Death.