Sidi Lamine gently opens the creaky wooden door that leads to his collection of manuscripts. Housed in a dark, windowless room, hundreds of medieval texts line handsome wooden bookshelves that reach to the ceiling. A musty smell lingers over everything. On an ornate table under dusty glass rest the rarest books in his collection, several of which he quietly mentions were written in 1010.

"I haven't visited this room in more than 10 months," he says, "because I was scared the Islamists would know that I have manuscripts like these, and they would destroy them. I thank God they are still OK."

Mr. Lamine, who says he's at least 70 years old and has been helping to preserve the texts since he was 10, recounts how Islamist militants took over this city recently, threatening the precious works. "Under the occupation," he says, "Islamists found families with manuscripts, and those manuscripts have not been seen since."...