Centurion (Latin centurio) is a commanding position (today one could say an officer rank) in the structure of the Roman legion of the Republic and Empire, located in the command structure below the military tribune and legate. During the Republic, the legion's centurions were elected primarily by soldiers. During the empire, a centurion was almost always appointed by a legion's legate. Centurion, as the name suggests, during the Republic period, commanded a centuria, a tactical unit of approximately 80-100 men. Two centurions in turn commanded the manipulator. During the Empire, the centurions also commanded cohorts, a tactical unit ranging from 500 to 800 men. During the early Empire, 59 centurions served in the legion, and the most important of them was Primus Pilus - the centurion most often with the longest service in the legion and the greatest combat experience. He held this position for a year and after that time he was either dismissed from his position or promoted. It is often assumed that during both the Republic and Empire periods, the centurions were the backbone of the legion.
Infantry in the Roman army has always played a great, even decisive role and in fact determined the outcome of the battles. During the early republic (6th-5th century BC), the Roman infantry probably used phalanx formation and was somewhat similar to units of this type in the Greek polis. However, in the course of the Samnite wars (4th-3rd centuries BC), it underwent profound changes, which probably led to the formation of three basic types of Roman infantry: triari (heavy armed, spear-fighting and most experienced infantry) hastati or principes (main mass of Roman infantry, armed with two pila, heavy shield and have) and velites (light infantry). At that time, the infantry used a manipulative formation. The Roman infantry shaped in this way also fought in the course of the Punic wars with Carthage (264-146 BC) or during the fights in the eastern part of Mare Nostrum. At the turn of the 2nd and 1st centuries BC, the Roman infantry underwent another reform thanks to the consul Mariusz. Its weapons and equipment were standardized, and shortly thereafter, the division into cohorts was introduced, and the Roman army itself - including, of course, the infantry - became professionalized. In the course of civil wars, the Roman army expanded quantitatively, but did not undergo fundamental organizational changes. It is worth adding, however, that probably at the end of the 1st century BC, lorica segmentata, the most famous and recognizable Roman armor, appeared in the equipment of legionnaires. In the period of the Principate (years from about 30 BC to about 235 AD) the regular army usually consisted of 28 to 32 legions, each of which numbered about 5,000 soldiers. During the crisis of the third century (235-284 AD) and in the Dominate era, the Roman army was expanded to probably approx. 400-500 thousand. people, and its armament has also changed. The production of helmets, shields and armor was simplified, and soldiers began to use new types of weapons, such as plumbata. It is conventionally assumed that the Roman army, until the Battle of Adrianople in AD 378, was able to relatively effectively face other opponents. Only after this battle does its dusk begin in the western part of the Roman Empire.