In the Imperial Roman army, a century in fact consisted of just 80 legionaries. Why not 100?
Originally, it was 100, but there were re-organizations, and the new size of a “century” came to be 80, but the name stuck.
I can bet some 1st Century Stand-up made that joke, along with “who was that Patrician I saw you with last night?- That was no Patrician, that was my wife”. 
http://members.aol.com/noctifer/private/Feyworld/DJ/GreatEmpire/Chap3/org.html#Decuria
No centuries usually had more than 100 men, though it could of possibly had less than 100 legionaires.
Budget cuts.
Actually, the century was based on Base 10. Hence it was easier for finger math for the centurion.
It’s the same reason Irish math is Base 7…
Damn farmers
It’s a nice site, but while it’s clearly based on Rome, I’m pretty sure it’s describing the fictional land of Zeth (check the link at the bottom and the history page from there).
How about here for a site which is about our Rome:
It doesn’t give a reason for the number being 80 but that leads on from the tent-party being 8, and presumably that was 10 before one of the many re-organisations of the army.
It got decimated ,lol
Declan
Redefinition of the size of army formations is a pretty common occurrence throughout history.
I believe in varied actually. It was not uncommon to a century to be on separate duty at an isolated post with supporting cavalry, archers and sappers attached.
Reminds me of this amusing quotation attributed to Heraclitus I ran across:
That’s always the case, even today. Go anywhere in the world where an army is deployed, and you’ll find an infantry company minus one platoon assigned elsewhere, reinforced by a two tanks and an engineering squad…
Sequestration. Rome was heading for a fiscal [del]cliff[/del] decline and fall.
One of the Roman emperors was missing a finger, so he decreed that the empire would henceforth operate on a base 9 system (9[sup]2[/sup] = 81, which is 80 soldiers + 1 centurion).
What?
IT COULD HAPPEN!
Everyone is assuming the name was originally accurate and the number of men was decreased. Maybe it was always 80 men, and the officers “rounded up” in calling themselves centurions because it sounded better. If you’re picking up chicks at the bar and your buddy starts bragging about how he commands “almost a hundred” men, are you going to be a stickler for accuracy and say you command eighty, or are you going to start telling folks you command “about a hundred”?
At a fundamental level, it’s around the limit one man can command using only voice. (Yes, a general can shout, “Forward!” and have thousands of troops move out, but he can only command that many through intermediaries, and 75-100 makes a natural break in the number one man can keep track of and effectively direct.)
That’s why even today, infantry companies are about 100 men strong.
Also, IIRC Centurion was a rank with many grades with differing responsibilities at each (like General today). You started with a Centurion in command of a Century, 80 men, went up to Centurion in command of about 500 men ( a cohort) unto the First spear centurion, who commanded nearly thousand men, the first cohort. In addition, Centurions also commanded attached archers and cavalry as well as the logistics troops of a legion, who would vary in number.
Fascinating.
ETA: “and 75-100 makes a natural break in the number one man can keep track of and effectively direct.” Debateable.
Maybe it’s for the same reason centipedes don’t have 100 feet and millipedes don’t have 1000.
Well, no. It’s not as if the people who gave the centipede its name also designed it.