I don't have the height in inches, but we talked about this last semester in my Vikings class -- the average Roman male was probably around 5'2" to 5'4", I believe, while Gauls, Saxons, Vikings and the like were closer to the height of the modern average man. (Too tall to be normal! So around six feet, maybe?)

(I think this may actually be mentioned in Tacitus, but I already packed my copy up to ship home.)