I'm making a man-at-Arms as a unique unit to replace the Axeman, since I think the axeman looks a little too barbarian-ish for my civ. The civilization is going to be a peaceful builder and I want the unique unit to help them survive the early game long enough to make a difference later, as opposed to someone like Washington who has trouble surviving to the end.

Does anyone have some suggestions for the abilities I should give it?

Depends. What civilization are you making it for?

The Gauls.

Well, from what little I know a Man-At-arms could have just about anything.It was also used to refer to a man who carried hand-weapons into combat during the medieval period He could have anything from a club to nun-chucks. To reflect that maybe you could give him a lot of little bonuses against everything. Maybe +10% vs. Melee, 20% Vs. Siege, 20% vs. Archers, or something like that.