Wouldn't it have been easier to use a roman calender if it was around that time? 
Probably, but us Jews are too cool for that. Even though the roman calendars went by the same cycle (lunar, like ours), for whatever reason it had slight, though important differences since exact time is important for us.
Not to mention that their months were named after different roman kings, while ours was based off of things in the bible. So we have to keep ours for traditions sake. The whole testimonial thing apparently went way back to biblical times though, and a rabbi named Hillel decided to just make an official calendar in about 350AC.
Even nowadays some rabbis refuse to go by the Christian Calendar, which actually makes sense at this point, though I'm too used to it to stop haha.
Anyway, holiday starts in about an hour and a half from now. Huzzah (this one isn't a fast, there's lotso food).
