The contubernium grouped eight legionaries who lived, cooked, and campaigned together without counting servants in that figure. Ten such groups formed the roughly eighty-man century, and six centuries formed a standard cohort. The enlarged first cohort brought a full legion's paper strength to about 5,280 legionaries before artillery, supply, and other attached personnel raised the marching establishment toward 6,000. These troops should not be imagined as permanently concentrated in one place. A main base might hold the first cohort and central support elements while other cohorts occupied subsidiary forts across the controlled territory. In operational terms, the legion could therefore resemble a division whose battalion-sized components operated independently or combined into larger groupings.
Chapter · 3:04:06-3:08:10
How a Roman legion was organized and dispersed
A legion grew from eight-man tent groups through centuries and cohorts, then operated as a distributed formation rather than one marching block.