A priceless 12th-century illustrated manuscript containing what has been described as Europe's first travel guide has been stolen from the cathedral at Santiago de Compostela in northern Spain.

The Codex Calixtinus, which was kept in a safe at the cathedral's archives, is thought to have been stolen by professional thieves on Sunday afternoon.

Archivists did not notice its disappearance, however, until Tuesday, when the cathedral's dean was told it was missing.

The local Correo Gallego newspaper reported that distraught cathedral staff spent hours searching for the manuscript before contacting police late that night.

"Although security systems have been improved considerably it is true to say that they are not of the kind one might find in a bank or a well-protected jewellers," the newspaper reported.

Only five security cameras were used to watch the archive area, according to the newspaper, and none were pointing directly at the safe where the priceless manuscript was stored.

Police reportedly believe that a black market dealer in antique manuscripts may have commissioned the robbery.

The codex was rarely removed from its safe, with researchers wishing to study it generally being handed a copy kept at the same archive.

The 225 parchment pages include a guide to the pilgrimage routes to Santiago, apparently written by a French friar, Aimeric Picaud.

They also tell the story of how St James the Apostle's body was supposedly transported from Judea on a raft without oars or sails, which swiftly crossed the Mediterranean and travelled north through the Atlantic before grounding in north-western Spain. From there it was supposedly dragged inland by two oxen, and the body was buried in a forest.

It was only eight centuries later, however, that locals began to claim the tomb of St James could be found there. Pilgrims eventually began to travel to the site, and an 11th-century pope declared that on certain years pilgrims could obtain plenary indulgence for their sins and so avoid purgatory.

The manuscript, apparently commissioned by Pope Calixtus II, helped popularise a pilgrimage that still attracts tens of thousands of people every year.

The author claimed pilgrims travelled from as far away as Scotland, Ireland, Wales, Jerusalem and Asia seeking "mortification of the body, increase of virtue, forgiveness of sins ... and the protection of the Heavens".

His guidebook also included warnings against eating some local fish which would cause you to "die soon afterwards or fall ill".