Priceless 12-century manuscript, which contains Europe's first travel guide, went missing from a safe in Spanish cathedral

A hugely valuable illuminated manuscript has disappeared from the cathedral of Santiago de Compostela in northern Spain, say police.

The Codex Calixtinus dates from the 12th Century and was compiled as a guidebook for medieval pilgrims following the Way of Saint James.

This is the oldest copy of the manuscript and is unsaleable on the open market.

Only a handful of people had access to the room in which it was kept.

This edition of the Codex Calixtinus is thought to date from around 1150.

Its purpose was largely practical - to collect advice of use to pilgrims heading to the shrine there. It also included sermons and homilies to St James.

On Wednesday afternoon, the book was reported missing from the room where it is kept.

"We are investigating its disappearance," a police spokeswoman said, according to AFP news agency.

"It is usually kept in a room to which only half a dozen people have access," she said.

The Codex is only brought out on special occasions, such as last year's visit of Pope Benedict, when it is closely guarded.

If the work has been stolen, it will be impossible to sell it on the open market, says the BBC's arts reporter Vincent Dowd.