Archimedes Palimpsest

Archimedes Palimpsest was found in a rare 10th-century Byzantine Greek
 manuscript, which is a palimpsest because it is a manuscript in which
 pages have been written on twice. As writing material was expensive
 an original text could be washed off so the parchment could be reused.
 The upper layer of writing on the document to be auctioned contains
 instructions for religious rites but underneath it contains versions
 of Archimedes' most celebrated Greek texts. In the Middle Ages,
 the work was owned by a monastery in Palestine whose collection
 was incorporated into the Greek Patriarchate library in Jerusalem
 in the 19th century. It was later transferred to a monastery in Istanbul.
 The work was taken to Athens when the monastery's library
was broken up after World War I.
source

http://www.archimedespalimpsest.org/

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