maiar,

 

Seven feet!  I don't know where you got those figures, but if I would guess that the average Roman was maybe 5"6"/150lbs.  The Praetorean Guard might have been 5'10"-6'0".

 

The average Celt was not 7'0"; more like 6'0"/180lbs, maybe.

No way 7ft, actually the average Germanic and Celtic tribesmen were slightly below 6ft. They averaged about 5'10"-5'11" but they still towered over their Roman counterparts who average around 5'3"- 5'4". Remember Ceasar was only 5'6" and he was considered tall by Roman standards.

 

So an average Roman soldier usually faced a tribal opponent who was 5-6 inches taller than him. Its like the mentioned example of 5'10" men vs the 6'3" men.

 

The tallest warriors to take part in combat in the ancient and modern world are I think were the Dinka and Masai warriors of East Africa, who are averaging 6'3" with tremendous reach advantage in hand to hand combact.  

Food for thought:

 

Lt. Audie Murphy, US Army, Medal of Honor holder and most decorated American soldier of WW2 was only 5 ft. 7 in. tall. 

 

Major Richard Bong, USAAF-Medal of Honor holder, P-38 scourge of Japanese Zero pilots in the South Pacific and America's top Ace of all time with 40 kills, was 5 ft. 6 in. tall.

 

The criteria I'd go for is a mentally and spiritually strong warrior with an aggressive, never-give-up attitude and not give a damn about his physical height.

Heavy infantry has typically been the biggest fellows, so they could tote the heavy equipment (Guard Regiments have typically been grenadiers). Where You stripped  the light infantry of anything but the bare necessities - and made them walk faster.  

The other factor has been to maintain an even length of pace in a unit, thus easing march.

 

I doubt these factor are that significant any more.

 

Incidentically: A B-52 pilot is typically a big man, as the big plane is a handfull.

Erm.. have you ever met a Gurkha?

Modern heavy infantry is in fact the opposite of the old heavy infantry; nowadays, heavy infantry have to squeeze into Bradleys, but have enormous firepower, so they tend to be small (from what I understand, not being a soldier).  Light infantry nowadays tend to be big and strong so they can hump their gear.

Umm...they're Asians! They don't count!

 

Whew, that was close.