A library is only as good as its collection, and the Ptolemies wanted everything. Stories about how they got their books range from ordinary purchases to tricks that look a lot like theft.

Buying

The simplest method was purchase. Royal agents traveled to Athens, Rhodes and other centers of Greek learning to buy books. Because the Ptolemies paid well, a market grew up, and with it a problem: forgers produced fake “old” copies of famous works to sell to the king's buyers. The doctor Galen, writing in the second century CE, complained that this had corrupted the texts of some ancient authors. Telling genuine works from forgeries became one of the library's scholarly tasks.

Aristotle's books

One later writer, Athenaeus, says Ptolemy II bought Aristotle's own library. Strabo tells a different story: Aristotle's books passed to a student's heirs in the town of Scepsis, who hid them in a cellar, where they were damaged before being sold and eventually carried to Rome. Both accounts cannot be fully true. Perhaps Alexandria bought some of the collection, or copies of it. The disagreement is a small example of a large problem: even the library's most famous acquisitions are known only through later, conflicting reports.

The books from the ships

Galen also tells the most famous story. Alexandria was one of the busiest ports in the Mediterranean, its harbor marked by the great lighthouse on the island of Pharos, one of the Seven Wonders of the ancient world. According to Galen, ships arriving in Alexandria were searched for books. Any found were taken to the library and copied. The library kept the originals and returned the copies to the owners. The seized books were labeled “from the ships.”

The Athenian deposit

Galen tells a second story. Athens kept official copies of the plays of its three great tragedians, Aeschylus, Sophocles and Euripides, so that actors could not alter the texts. Ptolemy III asked to borrow them for copying and pledged fifteen talents of silver, an enormous sum, as security. Once he had the scrolls, he kept the originals, sent back fine new copies, and simply let Athens keep the silver. The story may be embellished, but it shows how badly the kings wanted authoritative texts and how willing they were to bend the rules to get them.

Rivalry and parchment

Other kings built libraries too. The greatest rival was Pergamon, in what is now western Turkey, whose Attalid kings collected books and supported scholars. The Roman writer Pliny the Elder, quoting the earlier scholar Varro, tells a tale of this rivalry: a Ptolemy banned the export of papyrus to hurt Pergamon, and the Pergamenes responded by developing writing material from animal skin, which became known as parchment, from the Latin for “of Pergamon.” Historians treat this as a legend: parchment was already in use long before, though Pergamon may have improved or popularized it. The story survives because it is good, not because it is proven.

How big was the collection?

Ancient figures vary wildly. A Byzantine scholar named John Tzetzes, writing in the twelfth century CE but apparently drawing on older sources, reports about 400,000 mixed scrolls and 90,000 single scrolls in the palace library, and 42,800 at the Serapeum. The Roman writer Aulus Gellius, in the second century CE, gives 700,000. Modern historians are cautious. Some think the collection held a few hundred thousand scrolls at its height; others suspect the figures were inflated as the library became legendary. No one knows the true number, and an honest account says so.

Ethics of collecting

The library's methods raise questions that museums and libraries still face. Was seizing books from ships acceptable because copies were returned and knowledge was preserved? Was keeping Athens's originals a betrayal of trust? Today, debates over cultural objects taken by powerful states, such as the Parthenon sculptures in the British Museum, turn on similar questions of consent, ownership and whether preservation justifies possession.

Worked example: is the story true?

Take Galen's “books from the ships” and test it as a historian would.

• Who reports it, and when? Galen, a well-informed writer, but about four centuries after the events. He may be relying on tradition.
• Why does he tell it? In a commentary on medical texts, to explain why some copies of an old medical book carried the label “from the ships.” That detail suggests the label was real, even if the full story grew over time.
• Is it plausible? Alexandria was a royal port with strict control of trade, and the kings were known to spend heavily on books. A policy of copying books from ships fits the pattern.
• What would make us doubt it? No earlier source mentions it, and stories about powerful kings tend to grow more dramatic with retelling.

A fair conclusion: the story is possible and partly supported, but not proven. Compare that with the parchment legend, which conflicts with physical evidence of older parchment. Not every ancient story deserves the same degree of belief, and weighing them differently is the core skill of history.