Salisbury Cathedral is home to one of four surviving copies of the historic document, the Magna Carta. Issued by King John in 1215 as a solution to a political crisis he was facing.
It established for the first time the monarch was subject to the law of the land, rather than above it.
Although nearly a third of the text was dropped or substantially rewritten within ten years and almost all the clauses have been repealed in modern times, Magna Carta remains a cornerstone of the British Constitution and its principles are echoed in the US constitution and others around the world.
As well as providing a once-in-a-lifetime opportunity for researchers to study the documents together, the unification will be a chance for 1,215 members of the public to see the manuscripts side-by-side after winning free tickets in an public ballot.
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Holly has the forecast for tonight and tomorrow in the east of the region.
Holly has the forecast for tonight and tomorrow in the west of the region.