You can't exactly call it a reunion – the four surviving original copies of Magna Carta never before been in the same place.

So the British Library called it a "unification event" Monday when the priceless documents were put on display together for the first time.

The event marks the 800th anniversary of Magna Carta, which established the timeless principle that no individual, even a monarch, is above the law.

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In 1215, 40 rebellious barons came together to declare their rights to King John, and he reluctantly consented to their demands in an attempt to avoid civil war. It included acknowledgments that taxes cannot be arbitrary, that free men cannot be imprisoned without first being judged by their peers or the law and that justice cannot be denied or delayed.

But within weeks, the Pope voided the agreement, and England was thrown into war. The document was later incorporated into English law.

The original Magna Carta manuscripts were written and sealed in late June and early July, 1215, and sent individually throughout the country, making Monday's unification unique.

"It's a real moment in history," said Julian Harrison, the library's curator of medieval manuscripts. "Magna Carta has significance not just in England but worldwide. Many people regard it as the foundation of the rule of law. It established key principles which have resonated worldwide."

Officials said the three-day unification will give some lucky members of the public as well as constitutional scholars and medieval manuscript experts a chance to scrutinize and compare the documents.

About 1,215 people will be allowed to see the Magna Carta documents on Tuesday. They were randomly selected from more than 43,000 applicants from more than 20 countries.

Two of the documents are housed at the library, while the other two will return to their homes at the cathedrals of Lincoln and Salisbury.

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Later this year, copies of Magna Carta and its companion document, the Charter of the Forest, will go on a Canadian tour at museums in Ottawa, Winnipeg, Toronto and Edmonton.

Magna Carta influenced not only Thomas Jefferson when he helped draft the Declaration of Independence, but also the writers of the French constitution and the late South African leader Nelson Mandela, who cited it in his famous speech in his own defence at the Rivonia trial in 1964, Harrison said.

"This is a typical example of a statesman, as he later became, using Magna Carta as establishing civil rights as a universal touchstone," Harrison said.

With a report from Globe staff