In May 1844 and February 1859, Constantin von Tischendorf visited the monastery for research and discovered the Codex Sinaiticus, dating from the 4th century, at the time the oldest almost completely preserved manuscript of the Bible. The finding from 1859 left the monastery for Russia, in circumstances that had been long disputed. But in 2003 Russian scholars discovered the donation act for the manuscript signed by the Council of Cairo Metochion and Archbishop Callistratus on 13 November 1869.