The Library of Alexandria in Egypt, was once the largest library in the world. It is usually assumed to have been founded at the beginning of the 3rd century BC during the reign of Ptolemy II of Egypt after his father had set up the temple of the Muses, the Musaeum.
The Library at Alexandria was conceived largely as an attempt to bring together in Alexandria the whole of the earlier Greek science, art, and literature. At one point the Library held close to fifty thousand books.
The library was damaged, intermittently, several times, first by Julius Caesar, and finally destroyed by rioters. The loss of the Library, which contained the original (and sometimes only) copies of most of the ancient world's greatest works of literature, resulted in the decimation of ancient literature, and accounts for the modern paucity of ancient materials. Scholars estimate that historians now have only 1/10th of 1% of the ancient world's original source material to rely upon, as an almost exclusive result of the library's destruction. As an example, among the material lost in the library was a first-hand account of the life of Alexander the Great, written by his general and boyhood friend, Ptolemy. Historians know of the book's existence by citation to it, in secondary sources.