Roman forts were generally located in permanent military encampments
called castra. In English, the terms Roman Fortress, Roman Fort
and Roman Camp are generally used to denote these castra.
In classical Latin the word castrum denotes a legionary
encampment, whether temporary, semi permanent or permanent. A large
encampment was a castrum, and a small one a castellum (from which
we get the English word castle)
The best known type of castrum is the Camp. This was a military
town designed to house and protect the soldiers along with their
equipment and supplies when they were not fighting or marching.
More permanent camps were castra stativa, "standing
camps". Less permanent castra were castra aestiva
or aestivalia, "summer camps", in which the soldiers
were housed in tents. Summer was the military campaign season. For
the winter the soldiers retired to castra hiberna containing
barracks of more solid materials, public buildings and stone walls.
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 a few days. Even when
assembled, their open camps invited attack.
When legions were far from a permanent camp they needed to construct
a temporary castrum. Regulations required a major unit in the field
to retire to a properly constructed fort every day. To this end
a marching column carried in a baggage train of wagons and on the
backs of the soldiers, the equipment needed to build and stock the
camp. Camps were the responsibility of engineering units with specialists
of many types, officered by architects, "chief engineers",
who requisitioned manual labour from the soldiers at large as required.
An architect could throw up a camp in a few hours while under enemy
attack. Judging from the names, they seem to have used a selection
of standardised camp plans, selecting the one depending on the length
of time a legion would spend in it: tertia castra, quarta castra,
etc., "a camp of three days", "four days", etc.
The standard was a linear plan for a camp or fort: a square for
camps to contain one legion or smaller unit, a rectangle for two
legions, each legion being placed back-to-back with headquarters
next to each other. Laying it out was a geometric exercise conducted
by officers called metatores. The process started in the
centre of the planned camp at the site of the headquarters tent
or building (principia). Streets and other features were marked
with coloured pennants or rods.
The base fortification (munimentum) was placed within
a wall (vallum). The vallum was quadrangular aligned on
the cardinal points of the compass. Construction crews dug a trench
(fossa), throwing the excavated material inward, to be
formed into the rampart (agger). On top of this a palisade
of stakes (sudes or valli) was erected. Soldiers
carried these stakes on the march.
Over the course of time, the palisade might be replaced by a fine
brick or stone wall, and the ditch serve also as a moat. A legion-sized
camp always placed towers at intervals along the wall with positions
between for the division artillery. This basic pattern was to endure
long after the fall of the Roman Empire, being copied for centuries
in generation after generation of castle.
Around the inside periphery of the vallum was a clear space, the
intervallum, which served as an access route to the vallum
and as a storage space for cattle (capita) and booty (praeda).
Legionaries were quartered in a peripheral zone inside the intervallum,
which they could rapidly cross to take up position on the vallum.
Inside of the legionary quarters was a peripheral service road (Via
Every camp included a very wide main street, which ran through
the camp on a north-south axis. The names of streets in many cities
formerly occupied by the Romans suggest that the street was called
cardo or Cardus Maximus. Typically the main street
was the via principalis. The central portion was used as
a parade ground and headquarters area. The "headquarters"
building was called the praetorium because it housed the
base commander, praetor ("first officer"), and
On one side of the praetorium was the quaestorium, the
building of the supply officer, or quaestor ("seeker").
On the other side was the forum, a small duplicate of an urban forum,
where public business could be conducted. Along the Via Principalis
were the homes or tents of tribunes in front of the barracks of
the units they commanded.
At one end the Via Principalis passed through the vallum in the
"right principal gate” (Porta principalis dextra
) and at the other in the "left principal gate (Porta principalis
sinistra), which were gates fortified with towers (turres).
(Which was on the north and which on the south depends on whether
the praetorium faced east or west, which is one of the many details
of Roman camps that remains unknown.)
The central region of the Via Principalis with the buildings for
the command staff was a square called the Principia. Across
this at right angles to the Via Principalis was the Via Praetoria,
so called because the praetorium interrupted it. The Via Principalis
and the Via Praetoria divided the camp into four quarters.
Across the central plaza (principia) to the east or west
was the main gate, the Porta praetoria. Marching through
it and down "headquarters street" a unit ended up in formation
in front of the headquarters where the standards of the legion were
On the other side of the praetorium the Via Praetoria continued
to the wall,which it passed through the back gate (Porta Decumana).
Supplies came in through it and so it was also called the Porta
The street plan of various present-day cities still retains traces
of a Roman camp, for example Marsala in Sicily.
Due to local archaeology, the locations and layouts of Roman castra
are rapidly becoming known. Both amateurs and professionals are
involved in excavation and publication. Internet sites giving photographs
and the texts of inscriptions are numerous.