User blog comment:Mesi99/the title of the first episode/@comment-24385450-20140826160310

Of course, this is just a theory, but I think that the story takes place 2,000 years from now, (a.k.a. the 4000s,) but something happened in between that time that people felt the need to change the calendar. We know it wasn't the appearance of the Titans, because that happened after the calendar flipped. Perhaps it's something religious, like how our AD calendar has to do with Christ.