According to Islamic tradition, the Prophet Muhammad predicted that, just as the Jews and Christians had, the Muslims would split into a number of firqas (sects). 1 This prediction is reported in various versions, usually giving the number of sects into which Islam would divide as seventy-three, and usually consigning all save one to the fires of hell. 2 Since this prediction, various Muslim writers have compiled accounts of sects, sometimes called heresiographies by Western scholars. 3 The earliest known such work dates from the ninth century a.d.; Islamic heresiographies in more or less the classic format continue to appear today, and examples can also be found on the Internet. 4 Following the prediction of the Prophet, many Muslim heresiographers have devoted considerable ingenuity to ensuring that the sects they deal with number seventy-two (the seventy-third normally being the author’s own), evidently on two mistaken assumptions: that the number seventy-three should be taken literally, 5 and that no further sects would arise after the heresiographer’s own time.