Roman military engineering

The military engineering of Ancient Rome's armed forces was of a scale and frequency far beyond that of any of its contemporaries'. Indeed, military engineering was in many ways institutionally endemic in Roman military culture, as demonstrated by the fact that each Roman legionary had as part of his equipment a shovel, alongside his gladius (sword) and pila (spears).

Fabri were workers, craftsmen or artisans in Roman society and descriptions of early Roman army structure (Phalanx, the Legion came around the conquest of Greece) attributed to king Servius Tullius describe there being two centuriae of fabri under an officer, the praefectus fabrum.

Roman military engineering took both routine and extraordinary forms, the former a proactive part of standard military procedure, and the latter of an extraordinary or reactionary nature.

Each Roman legion had a military legionary fort as its permanent base. However, when on the march, particularly in enemy territory, the legion would, after a day's marching, construct a fortified camp or castra, requiring as raw materials only earth, turf and timber. Camp construction was the responsibility of special engineering units to which specialists of many types belonged, officered by architecti (engineers), from a class of troops known as immunes since they were excused from or, literally, immune from, regular duties. These engineers would requisition manual labor from the soldiers at large as required. A legion could throw up a camp under enemy attack in as little as a few hours. Judging from the names, they probably used a repertory of camp plans from a set textbook, selecting the one appropriate to the length of time a legion would spend in it: tertia castra, quarta castra: "a camp of three days", "four days", etc.

The engineers also built bridges from both timber and stone depending on required permanence, time available etc. Some Roman stone bridges survive to this day. Stone bridges were made possible by the innovative use of the keystone to allow an arch construction. One of the most notable examples of military bridge-building in the Roman Empire was Julius Caesar's Bridge over the Rhine River. This bridge was completed in only ten days and is conservatively estimated to have been more than 100 m (300 feet) long. The construction was deliberately over-engineered for Caesar's stated purpose of impressing the Germanic tribes, who had little experience of engineering, and to emphasise that Rome could travel wherever she wished. Caesar was able to cross over the completed bridge and explore the area uncontested, before crossing back over and dismantling the bridge. Caesar relates in his War in Gaul that he "sent messengers to the Sugambri to demand the surrender of those who had made war on me and on Gaul, they replied that the Rhine was the limit of Roman power". The bridge was intended to show otherwise.

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