Why do we shorten circa as ca.?

[Xyrec]

This is a thing that has always bothered me, why the hell do we do it? :regd09:

[Xyrec]

circa is a 5 letter word. It is already a short word.

[DrMelon]

[b]C[/b]irc[b]a[/b].
I can't really think how else you would shorten it.
Crc? Cc?
Well, not Cc as it is already shortform for "Carbon Copy".

[Extroll]

I like to shorten it to Circ-

[EmperorScorpious]

I have never seen it like that before. I've only seen it as "c.", no other way.