He commanded anywhere between 60 and 160 men depending on unit strength. Although he originally commanded 100 men this was eventually reduced to 80 (MOD cuts occurred even in ancient Rome). There were 66 centuries to a legion (the main Maneuver/administration unit of the Roman Army.
Centurions were allowed to ride on horseback during marches and (dependant on permission for marriage) to live with their family while in garrison.
There were six centuries to each cohort (480 men) and 10 Cohorts to a Legion. Each legion had a senior centurion (primus pilus -literally "first spear") who led the First Cohort which was usually double strength (960 men). The Second Cohort was commanded by the princeps secundus, and Cohorts Three to Ten were each commanded by a pilus prior. Theoretically there would be 9 cohorts each of 480 men plus 1 double strength cohort of 960 men plus 120 cavalry in a full-strength legion (5400 men). This number would vary as the decades passed and the legions reorganized.
Career Path of a Roman Centurion
Centurion Petronius Fortunatus who lived in the late 1st century and early 2nd century and who died aged 80 years old had the following service recorded on his tombstone (found at Lambaesis in North Africa. Lambaesis):
Enlisted in Legio I Italica in Lower Moesia (roughly modern Bulgaria). Over the next four years he held the successive posts of:
- Librarius (Clerk).
- Tesserarius (Guard Commander).
- Optio (2 i/c to the Centurion)
- Signifer (Standard Bearer).
Promoted to Centurion in the Legio I Italica by the vote of his comrades.
For the next 46 years he saw service as a Centurion with:
- Legio VI Ferrata in Syria.
- Legio I Minerva in Lower Germany.
- Legio X Gemina in Pannonia (Slovenia/Croatia/Hungary).
- Legio II Augusta in Britain.
- Legio III Augusta in Numidia (Algeria/Tunisia).
- Legio III Gallicia in Syria again.
- Legio XXX Ulpia in Lower Germany again.
- Legio VI Victix in Britain again.
- Legio III Cyrenaica in Arabia.
- Legio XV Apollinaris in Cappodicia (Eastern Turkey).
- Legio II Parthica in Italy.
- Legio I Aduitrix in Pannonia again.
At some point during this time he was decorated with a Mural Crown for being the first man over the wall of an enemy city as well as other decorations in the form of torques and phalerae.
He had a son, who pre-deceased him at the age of 35, and who was also a Centurion in Legio XXII Primigenia and Legio II Augusta.
(The Complete Roman Army, Goldsworthy, Thames & Hudson, 2003.)