Greetings from Jerash!
Like Petra, Jerash is another ancient city in Jordan that's popular with tourists. Though Jerash came much later than Petra, and by the looks of it, I suppose it's mostly Roman. Could have read all the signs along the way; didn't bother.
Local taxi drivers here are a bunch of fucking hustlers. The public transportation system is a joke. Buses hardly ever leave, and there's no schedule, so the taxi drivers are at you like zombies. They start by charging you three times as much as some will accept, but the ones who accept it don't exactly seem like they're the real deal.
When I learned that there are no bus routes to Ajloun and The Dead Sea, I immediately decided not to bother. I'll take The Dead Sea from the Isralean side whenever I get there, and the Ajloun Castle will have to join the ranks of all the thousands of castles that I might never see.
I wouldn't normally recommend this because it's usually much more expensive, but If you wanna go to Jerash, try to find one of those 1-day trip packages. Having to deal with taxi drivers here ain't worth the trouble.