HOUSTON (AP) — It was care fit for a king: The yellowing parchment was fitted inside a custom-designed aluminum and steel case with monitors, then wrapped in specially made packaging. Once it was on the plane, a canon chancellor nervously tracked the flight as it crossed the Atlantic Ocean.

That document, a rarely seen copy of the Magna Carta, had never before left England's shores and only once been outside its home in the Hereford Chapel near the Welsh border. Now, the famous charter, written nearly 800 years ago and considered one of the most important documents in the history of democracy, is safely ensconced in the Houston Museum of Natural Sciences, where it will be part of an exhibit that opens Friday.

"A very historic flight for us, and the cathedral and the document," said Glyn Morgan, chief executive of the Hereford Cathedral Perpetual Trust, who accompanied the document on its journey and is helping ensure it is properly cared for during its stay in Houston.

It will be on display for six months before being whisked back for a celebration of its 800th anniversary.

The Magna Carta was first issued on June 15, 1215, by England's King John in Runnymeade. The document was designed to prevent civil war by granting rebellious barons certain freedoms, including three that are enshrined in American government: an acknowledgement 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.

While scribes were hand-writing the Magna Carta in Latin, the king sent sheriffs and constables advance notice — or a writ — telling them to expect new royal orders. At the time, there were probably dozens of copies of this writ, but the only known surviving one is owned by a chapter of the Hereford Cathedral. That document, too, will be on display in Houston.

In the end, the Magna Carta didn't prevent civil war under King John because the pope nullified the charter shortly after it was issued. But two years later, after John died, his 9-year-old son, King Henry III, reissued the charter.

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This 1217 document is the one visiting Houston. The original folds from when it was delivered with two of the king's seals are still apparent. The iron gall ink made from oak tree acid has turned from blue, to black to brown over the years, the tightly scripted dialect of Latin that few people understand today.

Yet the ideas live on.

"Your life and the country you live in and this thing that you call the Constitution is influenced by this document, so this is a living document," said Dirk Van Tuerenhout, the museum's curator of anthropology.

Preparations to bring the Magna Carta to Houston have taken months, especially since the medieval document is only known to have left the cathedral's stone walls once before. During World War II, the Magna Carta, along with art from the National Gallery and other important documents, were put in "deep storage" in Aberystwyth, on the west coast of Wales, chosen with great secrecy to store Britain's treasures during the German attack on London.

In addition to the precautions taken during travel, caretakers of the Magna Carta need to ensure it is not exposed to great amounts of light — especially ultraviolet rays — or humidity, explained Chris Woods, director of the National Conservation Service. After the document's arrival in Houston on Feb. 3, Woods, Morgan and museum curators spent hours calculating the level of ultraviolet rays, trying to get as close to zero as possible.

A cavity underneath the case filled with silica gel — a chemical that helps regulate humidity — will prevent the parchment from wrinkling. Museum curators will check a sensor inside the case to ensure conditions don't change, and the room's temperature will be no warmer than 71.6 degrees Fahrenheit. A separate monitor will feed data to Woods' computer to become part of the permanent record keeping.

"I'll check each day," Woods said, who will return to England after the exhibit opens.

The museum, meanwhile, has prepared an exhibit designed primarily to convey to visitors — especially children — the document's importance and what life was like in the Middle Ages. There will be swords, knights, intricate stained glass replicas from a cathedral in Gloucester and models of the various kings' seals.

"This is intrinsically important and interesting," Van Tuerenhout said.

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Plushnick-Masti can be followed on Twitter at https://twitter.com/RamitMastiAP