GDG- Roman numerals

[Alan D. Brunelle]

I was (re)reading Tucker's Lee & Longstreet recently, and he pointed out 
- as I believe I've read elsewhere - that the notion of referring to 
various corps in Civil War armies by Roman numerals was a relatively 
recent thing. (At the time, the participants did not refer to them as 
such.)

In the context of Gettysburg, does anybody out there know the when, why 
and who started referring to the corps with Roman numerals? (Just curious.)

Thanks,
Alan