A legionary fortress was a large permanent base where a Roman legion lived, trained and was supplied. Latin writers call it a castra legionaria. Our map has no fort or legion layer, so fortresses are not drawn on it.
Key takeaways
- A legionary fortress was the fixed home of one legion, used for years at a time, which is different from a temporary marching camp [1].
- Fortresses sat in frontier provinces or in newly conquered land, and some later grew into towns.
- Our map has no legion or fort layer: its 9,348 Roman places come from the Pleiades gazetteer and are not a list of forts.
- To see the provinces a fortress would have stood in, open the map at AD 117 with provinces switched on.
How a legionary fortress worked
A legionary fortress was the permanent base of a Roman legion. Roman writers called it a castra legionaria [1]. Where a legion on campaign built a simple temporary camp each evening, a fortress was designed to last: it held barracks, a hospital, workshops, storerooms, a headquarters building and a bathhouse, and it was usually laid out as a neat rectangle with rounded corners.
Because a legion was a large body of men, about 5,000 of them in the early empire [1], a fortress was a small town in itself. Soldiers needed food, clothing, tools and entertainment, so traders, craftsmen and families settled just outside the walls. In some places these civilian settlements later became towns with their own rights. The stone and timber of the fortress itself was often reused when the army moved on.
Where the fortresses stood tells you where Rome felt its borders needed watching. They were placed along frontiers, in newly conquered territory or at points where a rebellion was likely. The frontier system as a whole, a border marker and defence system, is called the limes [2]. The homepage explains in why the borders are approximate that a frontier was a zone with troops in it, not a thin line.
A fortress was not the same thing as a smaller fort. Auxiliary regiments were usually housed in forts that were smaller than a legionary base, because an auxiliary unit was smaller than a legion. The words are sometimes mixed up in everyday English, which is why searches for "Roman fort" lead here.
An example from our data
The map does not draw any fortress, so there is nothing to click on. What you can do is see the provinces that held them and the road network that served them.
Britannia was annexed in AD 43 and covers 170,292 km² on our map, with 173 Roman places in the United Kingdom on the cities layer. Dacia, north of the Danube, was a frontier province beyond the main Roman world. Both sat on the edge of the empire when it reached 4.88 million km² in AD 117, and both needed an army on the spot.
The cities layer is the Pleiades gazetteer, which lists 9,348 ancient places across the Roman world. It is a list of places, not of forts, so a dot on the map may be a town, a port, a shrine or a station.
The thing people get wrong
People often assume that any Roman site with a rectangular outline and a wall was a legionary fortress. Most were not. Many were auxiliary forts, small signal posts, or the ordinary walled towns of provinces that had been settled peacefully. A legionary fortress is specifically the base of a whole legion, and there were only a small number of legions to house.
It is also wrong to think fortresses stood on the border itself. Many sat some distance behind it, so that the legion could move to whichever stretch of the frontier needed it.
Legionary fortress vs colonia
| Legionary fortress | Colonia | |
|---|---|---|
| Purpose | Army base | Chartered town of citizens |
| Who lived there | Serving soldiers | Citizens, often settled veterans |
| Status | Military | Highest civic rank a Roman city could hold |
Frequently asked questions
What is the Latin word for a legionary fortress?
Castra legionaria. The plain word castra means a camp or fortified base.
Can I see Roman forts on this map?
No. The map shows provinces, Roman places from the Pleiades gazetteer, main roads and modern borders, but no legions, forts or walls.
Did every Roman town start as a fort?
No. Some towns grew beside military bases, but many were old native towns, planned colonies or ports that had nothing to do with an army camp.
Sources
- Roman legion, Wikipedia.
- Limes, Wikipedia.
- Every figure from our own map is worked out from the datasets on the data sources page (checked against Ancient World Mapping Center outlines and Pleiades).