A few years ago, I noticed that "fanatic" comes from fanaticus: "inspired by a deity, frenzied, from fanum temple" and wondered who the god of fanatics might be. Bill Colsher left this comment:
Of course there's a goddess of fanatics! Two of 'em:
Juvenal uses fanaticus in Satire 4 with reference to Bellona and in the 2nd (along with Livy) with regards to the priests of Cybele. The word is actually pretty rare - Perseus showed only 18 instances, mostly in Livy and those mostly refer to the galli.
Bellona was a peculiarly Roman goddess of war. The sister (or wife or daughter) of Mars, her temple is where the senate would convene to meet with persons who could not enter the city, e.g. commanders still holding imperium. Her priests, in a Spring festival, would dance and stab themselves in the arms and shoulders with knives.
The galli, priests of Cybele, as is well known, would castrate themselves (presumably only once) in an ecstatic celebration on March 24th. Roman citizens were prohibited from joining this cult until the time of Claudius.