The most famous story about the Library of Alexandria is that Julius Caesar burned it down in 48 BC. It is a story everyone has heard, and it has the additional advantage of being mostly false. Caesar set fire to a shipyard in the harbor; the fire spread along the docks; some warehouses near the waterfront were burned, and possibly some books being stored in them. The main library complex — which sat in the royal quarter several blocks inland — was not on fire. Caesar himself wrote about the incident in his own war commentaries and did not mention destroying a library. None of the writers who saw Alexandria in the century after him mentions a destroyed library either. They mention the library, in fact, as a working institution.

So why does everyone know the Caesar version? Because two and a half centuries later, the Roman historian Cassius Dio (writing around 230 AD) said, in passing, that some books had been lost in the fire of 48 BC. Plutarch repeated the claim. Later authors expanded it. By the eighteenth century, in Edward Gibbon’s Decline and Fall of the Roman Empire, Caesar’s fire had become the event that destroyed the world’s greatest library.

It didn’t. There was no single event. The library died slowly, in pieces, across roughly six hundred years, and the modern question — who destroyed the Library of Alexandria — has a less satisfying answer than the various civilizational-villain stories that try to fill in for it.

What the Library actually was

The Library was founded sometime in the early third century BC under Ptolemy I or Ptolemy II Philadelphus — the chronology is disputed, but it was operating by around 280 BC. It was part of the Mouseion (the “shrine of the Muses”), an academic research institute attached to the royal palace in the Brucheion district near the eastern harbor. Books were stored in scroll form, on papyrus, kept on shelves in a series of halls that opened off a central colonnade.

It was not, by modern standards, one library. It was several. The main collection was at the Mouseion. A second, smaller collection — the “daughter library” — was housed at the Serapeum, the great temple of Serapis built by Ptolemy III on a hill in the western part of the city. There were probably also working collections in the royal palace itself, in private homes of the scholars, and possibly in subsidiary buildings around the Mouseion grounds.

How many scrolls were there? Ancient sources give numbers between 200,000 and 700,000. Modern historians, looking at the physical capacity of the buildings described, put the upper limit at perhaps 100,000 scrolls. Scrolls are not books. A typical scroll held the contents of what we would now call a single chapter or a single book of a long work. The Iliad, for example, would have occupied roughly 24 scrolls — one per book. Translated into modern reading material, the Library at peak probably held the equivalent of perhaps 30,000 to 50,000 books.

This is still an enormous number for the third century BC. It was, by some margin, the largest collection of texts ever assembled in the ancient Mediterranean. It was also a working research institution: poets and astronomers and mathematicians (Euclid, Eratosthenes, Aristarchus, Apollonius of Rhodes, Callimachus) were employed there on royal stipend.

What actually happened to it, in three slow acts

The fire of 48 BC is real. Caesar burned the Egyptian fleet at anchor in the harbor; the fire spread to dockside warehouses; some scrolls being stored there for export were destroyed. The number is uncertain — Seneca says 40,000 volumes, but Seneca writing a century later is not a great source for warehouse inventories. The main library was untouched. We know this because the geographer Strabo, who visited Alexandria around 25 BC (just twenty-three years after Caesar’s fire), describes the Mouseion as still functioning, with scholars in residence and a working collection.

The slow decline, 100–300 AD. Roman Alexandria was less interested in subsidizing Greek scholars than the Ptolemies had been. Funding shrank. Acquisitions slowed. The Mouseion is still mentioned in third-century texts, but as a smaller institution with fewer scholars. We do not know whether scrolls were lost to neglect, sold off, damaged by humidity, or simply allowed to disintegrate. We do know that by the time the Roman emperor Caracalla visited Alexandria in 215 AD and massacred a significant fraction of its young men, the Mouseion was already past its peak.

In 273 AD the Roman emperor Aurelian retook Alexandria from the rebel queen Zenobia. The Brucheion district — including, almost certainly, the original Mouseion buildings — was destroyed in the fighting or in the punitive demolitions that followed. After Aurelian, the main library is never mentioned again as a working institution. Whatever scrolls remained had to be moved to the Serapeum or distributed to private collections.

The destruction of the Serapeum, 391 AD. This is the event that pop-history sometimes calls “the burning of the Library.” It is more complicated and worse than the Caesar story. In 391 AD, the Christian patriarch of Alexandria, Theophilus, used a decree from the emperor Theodosius authorizing the destruction of pagan temples as legal cover to organize a mob attack on the Serapeum. The temple was demolished. The cult statue of Serapis was hacked apart. The pagan staff was killed, exiled, or forced to convert.

Whether the Serapeum’s library was destroyed in the same event is genuinely unclear. Christian chroniclers writing about the destruction of the temple mention pulling down columns and breaking statues, not burning books. The historian Eunapius, writing as a pagan, complains about the destruction of the temple but does not specifically mention the library. The most careful modern reconstruction, by Roger Bagnall, is that the library may have been destroyed along with the temple, or may have been removed and dispersed in the months beforehand, or may have already been gone by 391. The available evidence does not let us choose.

What is certain is that by the early fifth century, when the philosopher Hypatia was teaching in Alexandria, there was no Library of Alexandria to study at. She used private collections.

The Caliph Omar story

The fourth famous “destruction” of the Library is the Caliph’s fire of 642 AD: after the Arab conquest of Alexandria under the general Amr ibn al-As, the Caliph Omar is said to have ordered the city’s library burned, with the justification that if the books agree with the Quran they are superfluous, and if they disagree they are pernicious.

This story has the same structural problem as Caesar’s fire: it does not appear in any source from within five hundred years of the event. The earliest version we have is from the thirteenth-century Christian historian Bar Hebraeus, writing in Syriac in the 1280s — six and a half centuries after the supposed event. The Arab historians of the seventh and eighth centuries, who otherwise document the conquest of Egypt in great detail, do not mention it. The pious Caliph Omar quote does not appear in any contemporary Arab source. Modern scholars from both Arab and European traditions consider the story almost certainly a later invention, possibly an anti-Muslim Christian polemic, possibly a generic library-destruction trope.

By 642 AD, in any case, there was nothing meaningful to destroy. The main library had been gone for nearly four centuries. The Serapeum had been gone for two and a half. Whatever was left in Alexandria was private and scattered.

What survived

The work the Library of Alexandria did — the cataloguing, the editing of Homer, the geographical measurements, the astronomy, the mathematical proofs — survived not as scrolls but as copies of copies, carried west and east and translated repeatedly. Euclid’s Elements survived because medieval Arab scholars in Baghdad translated a Greek text that had been translated from an Alexandrian original. Ptolemy’s Almagest survived for the same reason. Eratosthenes’ measurement of the Earth’s circumference survived because Strabo cited it and Strabo survived. The actual scrolls are gone. The scholarship leaked out before the buildings fell.

There is no surviving fragment that can be identified as definitely from the Library of Alexandria. There are some sixth-century palimpsests in monastery libraries — the most famous being the Archimedes Palimpsest, rediscovered in 1906 — that may contain text copied from Alexandrian originals. We cannot prove this. The chain of custody is too long.

What remains of the Library is one stone. In 1995, French and Egyptian archaeologists excavating beneath the modern Bibliotheca Alexandrina found a section of inscribed limestone wall that may have belonged to the Mouseion’s east colonnade. The inscription is partial. It reads — in Greek — “…for those who love learning…” The rest is broken off.

It is the only physical trace left.