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A centuria (Latin centuria, from centum, “one hundred”) was a Roman military subdivision commanded by a centurion. A normal legionary century of the Principate is commonly reconstructed with an establishment of about eighty men. This is not a universal strength for the Republic, every auxiliary formation or the late Empire; actual numbers depended on casualties, replacements and detachments.
The military century and the century as a voting group in the centuriate assembly were different institutions despite their shared name.
| Unit | Typical composition | Approximate establishment |
|---|---|---|
|
Contubernium |
Legionaries sharing a tent group |
about 8 legionaries |
|
Century |
Several contubernia |
usually about 80 |
|
Cohort |
Usually 6 centuries |
about 480; the first cohort could be larger |
|
Legion |
10 cohorts, headquarters and specialists |
roughly 5,000, with variation |
The table describes a common model of a Principate legion, not a permanent headcount for every unit. Establishment, strength on the rolls and personnel present could differ.
The term “century” retained the idea of one hundred even as unit sizes changed. In a common Principate model, ten contubernia of eight men give approximately eighty personnel, and six normal centuries form a cohort. The first cohort had a special organisation whose evidence must be dated.
The optio, tesserarius, standard-bearer and other specialists belonged to the century’s military organisation. They should not automatically be added to eighty men as a fixed extra establishment. Servants and other attendants could accompany the troops, but their presence does not establish a universal century of exactly one hundred people.
A centurion commanded the century. His seniority depended on the century and cohort he led; the most prestigious centurion in a legion was the primus pilus of the first cohort. The optio served as deputy, the tesserarius handled the watchword and guard duties, and the signifer carried the century's standard.
The centurion enforced discipline, trained soldiers, assigned duties and led the unit on campaign and in battle. A century was at once an administrative group, a community of daily service and part of a larger tactical formation.
In the manipular legion, two centuries formed a manipule. The seniority of their centurions was expressed by the traditional labels prior and posterior. When the cohort became the principal tactical subdivision, centuries did not disappear; they remained the cohort's component units.
A century could receive a separate task, but normally operated within a cohort and legion. Comparing it with a modern company is therefore only approximate: command, supply and battlefield employment followed a different system.
In Roman politics, centuries were also the voting groups of the centuriate assembly. Tradition associated their organisation with Servius Tullius. Allocation took account of citizens’ property class and age. Citizens voted within their century, whose resulting decision counted as one vote in the assembly.
The groups did not contain equal numbers of voters. Their distribution and voting order favoured the wealthy: a majority could be reached before every group was called. The traditional total of 193 belongs to a particular arrangement of voting units, not to 193 military formations of one hundred men; the assembly’s organisation changed over time.
How many men were in a century? About eighty is a common establishment for an ordinary legionary century of the Principate. Actual strength and organisation in other periods could differ.
Why does its name mean “one hundred”? The name survived organisational changes and does not prove the unit’s headcount.
How many centuries made a cohort? A normal cohort had six in a common Principate model; the first cohort had a special structure.
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