The credit for the development of the Library of Alexandria goes to the pioneering spirit of the library's patron kings and to its first librarians, Demetrius and Zenodotus, for the amazing speed with which the library grew.
By the mid-third century BC, the original building was becoming too small and it was necessary to build a second building, located at the Serapeum.
The mother library endowed the Serapeum library with about 42,800 papyrus scrolls, either as a gift or as a loan in what was probably an attempt to ease the clutter of the older library by getting rid of copies and incomplete manuscripts.
The kings of Egypt became enamored with the library and with increasing its collection, sometimes through dictatorial means. Ptolemy the Third (247-222 BC), for example, forced all incoming travelers to Alexandria to hand in any books they carried.
If these books were not part of the library's collection, they were kept and their owners were given cheap copies on papyrus scrolls. Ptolemy the Third also asked the librarian of the Library of Athens to lend him the official papyri of the works of Aeschylus, Sophocles, and Euripides to have them copied and then returned.
Ptolemy the Third paid a deposit of 15 talents to be returned when the books were given back. However, he realized that the books were worth more than 15 talents, so he kept the originals and sent back copies to the Athens Library.