The House of Wisdom

I was reading tor.com today, and came across a piece about a comic called The 99, about a group of Muslim superheroes each of whom embodies the attributes of one of the 99 Names of Allah - and about the creator of the comic, Naif Al-Mutawa, who is at present on trial for heresy in Saudi Arabia.
Describing the background to the story in the comic, Naif Al-Mutawa talked about the Siege of Baghdad in 1258, by the Mongols, and the destruction of the Grand Library, or House of Wisdom. They said that so many books were thrown into the Tigris that it ran black with the ink, and red with the blood of the philosophers and scientists who were slaughtered.

Why had I never heard of this before?
Just about everybody (in the West, anyway) who loves books knows about the destruction of the Library at Alexandria, but this destruction seems to be on a similar scale and I'd never heard of it. Naif Al-Mutawa said that it was a well-known story to generations of Arabs, and a natural place for his story to start.

By the second half of the ninth century, according to Wikipedia, this Library had become one of the greatest hubs of intellectual activity in the Middle Ages, and the great scholars who were attracted to it established Baghdad as a major seat of learning. It was also linked to astronomical observatories and was a centre of translation of academic and scientific works, including many Ancient Greek texts. Mathemeticians there also developed algebra, and introduced the Hindu numerical system that we use today to the Western world.
Despite the great destruction of 1258 about 400,000 manuscripts were saved, by Nasir al-Din al-Tusi, and taken to Maragheh - but Baghdad, and Islamic scholarship and science, never really recovered.