About 357 CE the emperor Constantius II, son of Constantine I, aware of the deterioration of texts written on papyrus rolls, began the formation of the Imperial Library of Constantinople by having the Judeo-Christian scriptures copied from papyrus rolls onto the more permanent medium of parchment or vellum. The person in charge of the library under Constantius II is thought to have been Themestios, who directed a team of scribes and librarians that copied the texts of papyrus rolls onto parchment or papyrus codices. It is probable that this library preserved selected texts that survived the burning of the Library of Alexandria, though the historical accounts of the destruction of the Alexandrian Library are contradictory. It has been estimated that the Imperial Library of Constantinople eventually grew to about 100,000 manuscript volumes, presumably bookrolls and codices.
"The first indication of an imperial library in Constantinople comes from Themistius, who in an oration delivered in 357 congratulates the emperor on having undertaken to reconstitute and collect in Constantinople the literary heritage of ancient hellenism by having the works of ancient authors, including minor ones, transcribed by a cadre of professional scribes working at imperial expense (Or.4.59-61). Such a scriptorium and such a task presuppose a library, and the library, if not established by Constantius, owed its character and early development to him. Subsequently, according to Zosimus (Hist. nov. 3.11.3) the emperor Julian (361-63) lent his patronage to the library and enlarged its holdings with his own. The Theodosian code (14.9.2) informs us that in 372 the emperor Valens ordered the employment of seven copyists (antiquarii)--four for Greek and three for Latin texts--and some assistants to maintain and repair the books of the imperial library. Thus we know that the library housed both Greek and Latin texts, but not necessarily in separate libraries, as was the practice in Rome" (Gamble, Books and Readers in the Early Church. A History of Early Christian Texts  168).