Yahya of Antioch, writing a generation after, gives the churches destroyed under al-Hakim as thirty thousand. The figure is not arithmetic and was never meant as arithmetic; it is the scale of the thing rendered in the only register a chronicler had. The destruction was real and enormous — the Holy Sepulchre itself was levelled to the rock in 1009, which is why the rotunda the crusaders found is a rebuilding of 1048. Take the number as testimony to how it felt, and the rubble as testimony to how it was.
Chronicle (Dhayl)