Imperial Library of Constantinople

The Imperial Library of Constantinople, in the capital city of the Byzantine Empire, was the last of the great libraries of the ancient world. Long after the destruction of the Great Library of Alexandria and the other ancient libraries, it preserved the knowledge of the ancient Greeks and Romans for almost 1,000 years. A series of unintentional fires over the years and wartime damage, including the raids of the Fourth Crusade in 1204, impacted the building itself and its contents. Donald Queller notes that there is no indication of the continued existence of a formal imperial library at the time and no source mentions lost manuscripts. While there were many reports of texts surviving into the Ottoman era, no substantive portion of the library has ever been recovered. The library was founded by Constantius II who established a Scriptorium so that the surviving works of Greek literature could be copied for preservation. The Emperor Valens in 372 employed four Greek and three Latin calligraphers. The majority of Greek classics known today are known through Byzantine copies originating from the Imperial Library of Constantinople.
In ancient Greece the written word and most literature was transcribed onto papyrus. As the papyrus began to deteriorate there was a movement to transfer the reading material from papyrus to parchment as did Constantine the Great, around the 4th century, but his movement specifically concerned Holy Scripture. Constantine's heir to the throne Constantius II continued this movement. It was his work that culminated in the first Imperial Library of Constantinople. The library is estimated to have contained well over 100,000 volumes of ancient text. The movement was headed by one Themistios, who commanded a group of calligraphers and librarians.

Wikipedia