[kbs666]

*twitching*
Calendars are important because they tie everything else together. I have this huge backstory of my campaign world covering thousands of years of history. Different ages of the world are dated by the dominant race of the time, Dragons, then Elves and finally Men. Then there is the weirdness of lunar calendars, The world has 3 moons. so different nations and cultures base their calendars on different moons, the moon chosen has a lot to do with the preferred magical style of the nation's leaders as each moon is tied to the different styles of magic.

So for example in the Dragon ages there are 2 primary calendars, The metallic dragons calendar which based their calendar on the prepared caster moon, they are mostly clerical casters, while the chromatic dragons calendar is based on the spontaneous moon, they are mostly sorcerers. They also have different year dating schemes. the metallic's begin the roll of years from the first clutch of eggs of Bahamut and his mate. The chromatic's begin their dating with the slaying of Bahamut's mate by Tiamat. So the two calendars are several centuries out of sync.

It gets more complicated from there.