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Reconstruction of the defenses of a roman mobile castra

Available translations: italiano (con note storiche addizionali)

Experiment's targets

Following the list of the main goals:
1) verify the necessary time to create the temporary defenses of a one-night camp, with a minimum size trench (depth: 3 feet and width: 5 feet), according to the available manwork;
2) verify most the effective way to dig the trench, to build the embankment and to manage the manworking;
3) test the effective roman tools reconstructed following archeological evidences;
4) test the defences with an enemy attack from outside the field.

Operating results

1) According to Polybius, in the repubblican era the allies were in charge to build the defenses on the sides where they were lodged (porta principalis dextra and sinistra), Romans were in charge to build the remaining sides (porta pretoria and decumana), one side per legion. Each side of the field, (2150 feet long, was divided into a number of parts in correspondence of the numer of the maniples in charge. If the field was located in the enemy territory, only a part of the maniples (for instance the half or less) were used in the works, while the other part and the cavalry were deployed on guard duty. In the case of a very dangerous location romans could have been used only 1/3 of the manworking (10 maniples of 30), each maniples would work on a 2150/10=215 feet front line (63 metres). These means that, considering not all the members of a maniple were at work in the same time, on each metre were working two men as average.
It is said in the DMC, about the imperial time, something similar to this average: the field described by Pseudo-Hyginus, for three legions, four praetorian cohorts and various auxiliary units (about 45,000 men), has a 7940 feet perimeter. Considering a working force of 15,000 men (about 1/3 of the total) the average of about two men per metre is confirmed.

It is supposed that the normal achievement required two or three hours maximum. If we consider a perimeter 8,000 feet long, and a "V" trench 5x3 feet width x depth produces 0.7 mc of heart, it should be digged 5,600 mc. Considering each man able to dig 0.5mc/hour of land, a total of 11,200 men could be needed to make the trench in one hour, or 5,000 men in two hours.
We could think that normally in 1-2 hours, romans were able to build all the necessary defenses, prior to all the other duties inside the field as tents, etc. In fact if we consider a normal day of march (5 hours of march with the necessary stops) and the necessity of a proper rest it was not possible longer times as a rule.
In our experience the trench has been deployed on a 50 metres front line, including also one of the fields ports (the principalis sinistra) created building a small clavicola to access to the field.
The ground were we tested was very soft, perfectly able to drain and basically with no rocks. The ground was sloped according to the suggestions of Polybius and Vegetius. The drain of the soil was hardly tested during the heavy storms of both the nights.

The trench has been done according the "V" section-profile ( fossa fastigata), 5 feet wide at the ground level and 3 feet deep (1.5 x 0.9 metres). Excavated earth produced an amount just a bit over 0.7 cubic metres for each metre, and has been used to build an embankment (agger) with a 1.4 x 0.6 x 0.7 metres cross-section (lower base, upper base, height). The experience demonstrated that the embankment, should be renforced with stronger materials as stones or wooden poles.
With 25 not trained men, the work requested about 8 hours during two days.
If 100 men were available (two men each metre) we could assume the work to be finished in a couple of hours, basically as assumed in our study.

2) After to have verified more than one solutions, these are the conclusions:
- while digging each man needs not less of two metres to easily move, much better three;
- it is useful to divide the digging line into different sections three metres long. Each section has to be assigned to a couple of men, one with shovel and turf spade and the other with the dolabra: they will work in rotation;
- the men not directly involved in the digging operations can be used to found/prepare additional materials such as poles, branches, etc. They will be used to make the embankment stronger. Otherwise they will help to transport ground filled baskets.;
- during the excavation, the normal garments or the armours didn't create any trouble. None of the men has complained for movement troubles while working with the lorica segmentata, a part some non relevant small haematomas due to not correct armour size. Also the gladius always carried has not created any problem.

3) Tools used: mainly dolabra, but also shovels, turf spades and hoes, replicas of some common archeological findings. Some of these tools (i.e. the turf spade) were hand forged; some others simply modified starting from similar modern pieces.
The turf spades, has been revealed as unuseful on soft terrain like the one tested.
The dolabra was very useful also to enlarge the trench, while "cutting" the ground in presence of big roots.
We didn't use baskets, just some attemps were made only for testing. We preferred to move ground directly with the shovel, but it is clear that in case of bigger or deeper excavations there is no other way that to use them.

4) We tested the vertical poles fixed in the ground and binded with ropes. Many problems appeared. The first issue was the effective way to plant them without to damage them: the double spike at both ends doesn't allow to use a club or a hammer. So we did it by pressing it simply with the hands.
The ropes used were hand made of natural canvas. They demonstrates strong resistance even if heavily wet due to the storms and the mud.
Dut to the heavy wether conditions we had not time to test the effective resistance of the entire defence with the simulation of an enemy attack, but the general impression was that vallis vertically planted in the soft earth, can offer only a fair protection and easily cave under an assault even if binded properly.
We tested a different solution for the vallis by planting them 45 degrees inclined. Looking at the result the feeling is that this way they could make much difficult an assault.
A third solution to mount them as "stars" could be effective too even if a bit more complicated to be mounted.
We tested also a 3 metres height palisade only 4 metres long above the trench. This solution could have been used for longer staying. In this case has been left a wider area between the "V" slope and it has been excavated a second small trench 3 feet deep in order to host the big poles. The excavated ground from the vallum has put just behind the palisade and "hammered" to be stronger and create the internal agger.

Giuseppe Cascarino

english traslation by Luca Bonacina



All the activities took place in the area between CastelGandolfo and Albano Laziale (very close to Rome) in september 2005 from 16th to 18th.
These are the groups that have contributed to the tests (in alphabetical order):
Cohors I Praetoria - Associazione Romars
Cohors III Praetoria - Associazione Culturale Cisalpina
Legio XXX Ulpia - Legio XXX Ulpia Traiana Victrix ONLUS


Bibliographic Notes
1 - Virgilio, Eneide (7, 126)
2 - Plutarco, Phyrrus (16-5)
3 - Polybius, Historiae (VI, 26-42)
4 - Flavius Josephus, Bellum Judaicum (III, 86-87)
5 - Caius Julius Caesar, Commentarii De Bello Gallico (VII, 72-74),
6 - Flavius Vegetius Renatus, Epitoma Rei Militaris (I, 21)
7 - Flavius Vegetius Renatus, Epitoma Rei Militaris (I, 21-25 e III, 8)
8 - Flavius Vegetius Renatus, Epitoma Rei Militaris (III, 8)
9 - Flavius Josephus, Bellum Judaicum (III, 5, 1)
10 - Polybius, Historiae (XVIII, 18)
11 - Livius, Ab Urbe Condita Libri (XXXIII, 5)
12 - Cassius Dio (XVII, 63)
13 - Caius Julius Caesar, Commentarii De Bello Civili (I, 42)
14 - Livius, Ab Urbe Condita Libri (XXXIII, 6)
15 - Junkelmann, Die Legionen des Augustus
16 - Caius Julius Caesar, Commentarii De Bello Civili (III, 67)
17 - Caio Sallustio Crispo – Bellum Iugurthinum (III, 36)

Additional bibliography
Hyginus Gromaticus – Liber De Munitionibus Castrorum (DMC)
Plutarco – Vite parallele
Pseudo Cesare – Bellum Africum (B.Afr.)
Pseudo Cesare – Bellum Alexandrinum (B.Alex.)

Studies on the roman field defenses:
Fabricius, Ernst – Some notes on Polybius’s descriptions of Roman camps – JRS, XXII, 1932, pp. 78-87
Gilliver, Catherine M. - Hedgehogs, caltrops and palisade stakes - Journal of Roman Military Equipment Studies, 4, 1993, pp.49-54
Junkelmann, Marcus - Die Legionen des Augustus: der römische Soldat in archäologischen - Mainz am Rhein, Philipp von Zabern, 1986
Lenoir, Maurice - Des fortifications du camp / Pseudo-Hygin; texte etabli, traduit et commente – Paris, Les belles lettres, 1979
Miller, M.C.J e Devoto, James Garry - Polybius and Pseudo-Hyginus: the fortification of the roman camp – Chicago, Ares, 1994
Peddie, John - The Roman war machine – Stroud, A. Sutton, 1994
Salvatore, John Pamment - Roman Republican Castrametation:a reappraisal of historical and archaeological sources – Oxford, B.A.R. 630, 1996


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