The Roman Castrum: Construction and Setup Process

The Roman castrum was designed as a temporary defensive structure that protected a legion’s supplies and rested its soldiers. While on long marches, legions would set up a castrum every night and disassemble it in the morning. Castra were a representation of the Roman’s ideal city brought down from the heavens. As a result, Roman castrumswere maticulously made perfect in every way. From an even wall, to roads that followed the cardinal points perfectly, to a seamless vallum (defensive wall). The Castrum was an important part of the Roman military and a reflection on important Roman values, and therefore were constructed with the utmost precision while still keeping its mobile properties.

Kit of Parts

Each roman legion marched with a unit of engineers and carpenters led by a Chief Engineer or Architecti. They carried with them, tools for building and measure, stakes for building the perimeter wall, tents for barracks, and a meritte of other equipment for erecting the structure both quickly and precisely. A Roman castrum must be able to be erected in a few hours even when under attack. A caravan often followed a marching legion inorder to help carry this huge load. The equipment varied with the needs of the legion and the seasons. There were summer camps or sub pellibus tentoriis, winter camps or castra hiberna, camp of 3 days or tertia castra and 4 days or quarta castra, among many other variations.

Set-up/ Construction

When erecting a castrum, the first step of the process is to find a site. The site must be flat, not be vulnerable to attack, and ideally have running water for hydration of both soldiers and animals and to act as a base for the latrine.

Once a preferred site is found, engineers started plotting out the site. This usually started at the center of the camp, graduated measuring rods or decempedae and sighting devices or groma accurately measured out the two main perpendicular roads and aligned them perfectly with the cardinal points. Streets, gates, and important features were marked out with coloured rods. Once features are marked, the grunt work begins. A trench is dug out around the parameter. The dirt from the excavation is not wasted but placed inside the vallum for further fortification. Stakes were erected to make up the vallum. When desired, towers were placed at intervals around the parameter for additional defense. Permanent camps required the structure to be made with materials with greater rigidity and durability. Stone and brick could be quarried from surrounding areas. All in all, Roman castra were a precise piece of engineering that was both easy and quick to set-up and also provided a considerable level of defense.