A castrum was designed to house and protect the soldiers, their equipment and supplies when they were not fighting or marching.

The camp allowed the Romans to keep a rested and supplied army in the field. Neither the Celtic nor Germanic armies had this capability: they found it necessary to disperse after only a few days.

From the time of Augustus more permanent castra with wooden or stone buildings and walls were introduced as the distant and hard-won boundaries of the expanding empire required permanent garrisons to control local and external threats from warlike tribes. Previously, legions were raised for specific military campaigns and subsequently disbanded, requiring only temporary castra. From then on many castra of various sizes were established many of which became permanent settlements.

The street plans of various present-day cities still retain traces of a Roman camp, for example Marsala in Sicily, the ancient Lilybaeum, where the name of the main street, the Cassaro, perpetuates the name "castrum".

The Centurion, or company commander, had a double-sized tent for his quarters, which served also as official company area. Other than there, the men had to find other places to be. To avoid mutiny, it became extremely important for the officers to keep them busy.

This ideal was always modified to suit the terrain and the circumstances. Each camp discovered by archaeology has its own specific layout and architectural features, which makes sense from a military point of view.

The streets, gates and buildings present depended on the requirements and resources of the camp. The gates might vary from two to six and not be centred on the sides. Not all the streets and buildings might be present.

Activities conducted in a castra can be divided into ordinary and "the duty" or "the watch". Ordinary activity was performed during regular working hours. The duty was associated with operating the installation as a military facility. For example, none of the soldiers were required to man the walls all the time, but round-the clock duty always required a portion of the soldiers to be on duty at any time.

In addition were special guards and details. One post was typically filled by four men, one sentinel and the others at ease until a situation arose or it was their turn to be sentinel. Some of the details were:

Below are a number of links to sites reporting or summarizing current research or thinking. Many are reprints of articles made available to the public at no charge. The historical researcher will find their bibliographies of great interest.