Magna Carta

"The myth of Magna Carta lies at the whole origin of our perception of who we are as an English-speaking people, a freedom-loving people who've lived with a degree of liberty and under a rule of law for eight hundred years. It's a load of tripe, of course. But it's a very useful myth."

Nicholas Vincent, a professor at the University of East Anglia and author of a book on the document.

The BBC has an article about celebrating that myth:

Magna Carta went on to change the world, British Prime Minister David Cameron said at an event marking the eight hundredth anniversary of the document that heralded modern democracy. He was speaking at a ceremony at Runnymede in Surrey, close to the River Thames, where King John of England sealed the original document in 1215.
The Queen (photo, second from right) also attended the ceremony.
The charter first protected the rights and freedoms of society and established that the king was subject to the law.
Cameron told the audience that Magna Carta altered forever "the balance of power between the governed and the government". He said the document had inspired different generations and countries across the world. He said: "Why do people set such store by Magna Carta? Because they look to history. They see how the great charter shaped the world, for the best part of a millennium, helping to promote arguments for justice and for freedom."
Archbishop of Canterbury Justin Welby (photo, left) said the document "set the bar high for all of us today". 

Analysis by Peter Hunt, BBC diplomatic and royal correspondent:

For a document credited with delivering so much, this was a brief celebration, limited to a few speeches and musical performances.
Where powerful rebellious barons and a king had once sealed the Magna Carta, sat a Queen whose powers and those of her many ancestors were limited by the eight-hundred-year-old text.
The Latin text, written on sheepskin, failed to avert a civil war.
Today, in the meadow by the River Thames, the prime minister used it to highlight a future battle: the one to come over his government's plans to replace the Human Rights Act with a British Bill of Rights.
Reform, which will be contested, is for the future.
Today, the focus was more on the past and celebrating Magna Carta, which is revered and has had influence in America and at the United Nations; and which is considered by many to represent the foundation of democracy.

Why is Magna Carta so important? The BBC has a column by  Clive Coleman, legal correspondent:
"Does Magna Carta mean nothing to you? Did she die in vain?" asked an exasperated Tony Hancock, playing the jury foreman in an episode of his famous Half Hour.
Clearly not. Far from dying, Magna Carta has had a life longer, fuller, and more influential than the most optimistic medieval baron could have imagined.
But why is a charter from 1215, which was declared null and void by the Pope within weeks of being written, which doesn't mention "trial by jury" or habeas corpus (the right not to be held indefinitely without trial), and which forbids any woman from accusing a man of murder or manslaughter, seen as the foundation of our liberties and our law?
At its heart is the idea that the law is not simply the whim of the king, or the government. It is the great egalitarian legacy of Magna Carta, that all are equal under the law, and all can be held to account. It is that idea that gave birth to so many of our rights and freedoms, to parliamentary democracy, fair trial, and a series of controls on the abuse of arbitrary power.
There will also be a rededication of the American Bar Association's Magna Carta Memorial.
A replica of the Great Charter began its journey down the Thames as part of the commemorations.
The Royal Barge Gloriana has led two hundred boats from Hurley in Berkshire and is due to arrive at Runnymede on Monday.

There are just four known copies of the original Magna Carta in existence today, from an estimated thirteen that were made. Two are held by the British Library, with Salisbury Cathedral and Lincoln Cathedral holding the others.

Rico says we have the same myth, we just call it the Constitution...