Ptolemy I Soter wanted to create a city of the mind. He wanted Alexandria to be the intellectual capital of the world. That being said, he didn’t initially have any plans for a big library. He was mainly collecting books to write a biography on Alexander, and eventually kept expanding the scope, until deciding to build the big library.
He may have come up with the plans for the library, but his son, Ptolemy II, was the one who actually got it built. The goal of the library was very ambitious – “unlike its rivals, the new library was to be universal. It would aim for complete coverage of everything ever written.” (source)
There are interesting stories about the methods that were used to acquire books for the Library of Alexandria. In one account, it is said that boats arriving at Alexandria would have all of their books seized and copied. The original would be kept in the library and the copy would be returned to the owner.
People were sent out by the library to go buy books wherever they were available. Additionally, they would borrow books from other libraries and make copies before returning them.
It is unclear how much of these accounts are true, or how exaggerated they are, but suffice to say, they put in a lot of effort to acquire books.
As for how many books were actually in the library, this is a highly debatable question. There are a lot of primary sources on this, all with vastly different values.
In a lot of the content on the Library of Alexandria, people just choose the highest number because it sounds more interesting. The estimates range from 40,000 - 700,000 scrolls.
The library was actually part of a larger institution called the Musaeum, which is a temple of the Muses. Instead of imagining a huge library building, it would be more accurate to think of the Musaeum as a university campus. There were different buildings and rooms for different things, and the library was a part of that.
There’s no existing description of the library, but we do have a description of the Musaeum from Greek geographer Strabo.
“The Museum is a part of the palaces. It has a public walk and a place furnished with seats, and a large hall, in which the men of learning, who belong to the Museum, take their common meal. This community possesses also property in common; and a priest, formerly appointed by the kings, but at present by Cæsar, presides over the Museum.” (source)
There was a dorm, a dining hall, lecture halls, the library, and more – all the things you would expect from a university campus.
Official scholars of the Musaeum were paid a good salary, didn’t have to pay any taxes, and got free housing as well as free food (source). It’s no wonder that the intellectual environment flourished in Alexandria. The only thing these scholars had to worry about was the pursuit of knowledge.
This may be one of the biggest historical misconceptions of all time, so I’m going to put it in all caps just to make it clear: THE LIBRARY OF ALEXANDRIA DID NOT BURN DOWN.
Alright, so what happened to it?
Life would be a lot easier if we could point to one person or group and put all of the blame on them, which is why we tend to do it so often, but the truth is more subtle.
The city of Alexandria dealt with a lot of political instability, and various groups fought over the city. There was a declining focus on intellectual pursuits from the city’s leadership, and the Musaeum probably lost funding and prestige over time.
“The later Ptolemies, those who held the throne from the middle of the second century B.C. on, were confronted with increasing social unrest and other problems and the library no longer enjoyed the attention their predecessors had lavished on it.” (source)
When you mix the loss of funding with a declining intellectual environment, and constant political instability and fighting, then you get a slow decline over time. And so, the greatest library of all time died a slow death, fading into obscurity until it was no more.