My guidebook tells me the mosque was completely rebuilt in 1908-1913, but I have the strong feeling it has since been rebuilt again, the one I saw looked brand new. At any rate, it contains the (reputed) tomb of one of the early followers of Muhammad, Khalid Ibn al-Walid, whose military campaigns, again according to the guidebook, led to the Islamic conquest of Syria. He died in 642, his exploits were exclipsed by his sworn enemy, the Caliph Umar.