I'm reading Ernle Bradford's Hannibal, and he mentions the difficulty the Romans had pushing around ~80,000 men, because it was twice their usual maximum. Four legions, or around 40,000 men, is the most they'd ever have in one spot. Why was that?
I know the simple answer here is "four legions was usually more than enough." I'm just wondering if there's an extra interesting reason to do with, say, maximum audible range of signalling trumpets.
Thanks.
Two legions was legally the maximum number of troops that a consul could command. To my knowledge there's never been any explanation given for the size of a consular army, but the law was extremely old, in place by at the latest the Samnite Wars. Even in the earliest period we see that in all likelihood two legions was the maximum--the earliest legions were levies of a thousand men from each of the three tribes (so 3000 total per legion), commanded by a praetor, later a consul, which would place the limit at two total. Two consular armies marching together would comprise the army of the state as a whole, a force of four legions. Later this was amended, so that a consular army consisted of four legions, which is also what a proconsul received from the state--Caesar went into Cisalpine Gaul with four legions, and raised an additional two before crossing the Alps.
maybe someone can clarify as some what unrelated..... A legion was 5000 men in Imperial Roman eras after basically all of the Marius reforms. Every book I've ever read about the first century invasions of Britain or Gaul, always have legions as 9 or 10 Cohorts of 460 men broken down to centuries of 80 men, With the first Cohort being double size (if there were only 9 cohorts).
It was my understanding that some battles had in excess of 15 legions based on how many losses they had.
was it different during the Republic era because I had thought that some of the major battles with Hannibal had 10 legions present?
Although it's never mentioned directly in any source material I've read, the reason is most likely difficulty supplying and organizing such a large body of men. Adrian Goldsworthy talks about this in "Caesar" when contrasting the Roman army with the tribal armies Caesar fought in Gaul. Organizing an 80,000 man army would have definitely required a double consular army (or a dictator), and was only possible during the Punic Wars when Rome was fighting hannibal in Italy itself (making supplying the troops much easier then if they were in Spain, for example).