The fear is raised weeks after the institution was told by a government advisory panel that a 12th-century manuscript in its collection was looted from a cathedral near Naples during the Second World War and must be returned.

The backing last month by the Spoliation Advisory Panel of a 27-year campaign by the city of Benevento to be reunited with a jewel of Italy’s heritage will have given renewed hope to St Catherine’s, a desert monastery on the Sinai Peninsula in Egypt, of being reunited with a manuscript that it is believed to have owned from the 6th century, if not earlier.

The 4th-century Codex Sinaiticus, arguably the world’s most important Christian manuscript, entered the library’s collection in the 1930s.

It is so old and fragile that only four scholars have been given full access to it in the past 20 years.

Greek Orthodox monks of St Catherine’s have long believed that the manuscript was wrongfully taken from them in the 19th century by a German scholar, Constantine Tischendorf, who was apparently acting as an agent for Tsar Aleksandr II of Russia.

He took 43 leaves to Germany, which are in the University of Leipzig, and another 347, which he gave to the Tsar.

They remained in the Imperial Library until 1933, when the Soviet Government sold them to raise money. The manuscript was bought by the British Museum Library, now the British Library, for £100,000, then a record sum for a manuscript or book. A public appeal raised the money to purchase it. Such is the Bible’s importance that it would exchange hands today for tens of millions of pounds.

Tischendorf is thought to have convinced the monks that he was borrowing the leaves for copying purposes. He did publish the text.

In an 1859 letter, which was found in the monastery’s archives in 1960, he had promised to “return (the Codex), undamaged and in a good state of preservation, to the Holy Confraternity of Mount Sinai at its first request”. But the ownership question is clouded by another letter, of 1869, in which the monastery’s archbishop seems to have offered the Codex as a gift to the Tsar, after a donation of money and gifts to the monastery.

The precise circumstances of the manuscript’s removal will be researched as part of an unprecedented collaboration between St Catherine’s Monastery, the British Library, the University of Leipzig and the National Library of Russia in St Petersburg.

ANCIENT TEXT

• Written in Greek on vellum around the time of Constantine the Great
  
  
• Contained the entire Old and New Testaments and the Apocrypha, but half of the Old Testament has been lost
  
  
• Surviving manuscript concludes with two early Christian texts, an epistle ascribed to the Apostle Barnabas and the Shepherd of Hermas
  
  
• The Monastery of St Catherine in Sinai, Egypt, is one of the longest continuously active Christian monastic communities

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