the century - fighting unit

[Tarbicus]

Hib and Brian, I think you might have both hit the nail on the head. If we go back to the formation of legions, they tended to be militia who elected their centurions IIRC. If there was no splitting up during selection at the time of the kings, then the whole land and community grouping makes sense if the centurion was seen as a leading man from a community, and an obvious candidate to be elected.

I think it ties in well with the Roman army's origins as a war band.