3.3 Military population and their associates
An estimate was made of the size and composition of the Roman army and the associated vicus population, in order to gain an impression of the required amount of food. Based on their rather small size, it is assumed that the forts could house one cohors, circa 480 soldiers, but a number of soldiers per fort lower than 480 is likelier (Bechert 1983; Glasbergen & Groenman-van Waateringe 1974; Polak et al. 2004). De Weerd (2006) even argues that the forts were only occupied in the first century when it was necessary. The absence of vici in this period supports this hypothesis. Graafstal (in press.), however, has convincingly argued that the army controlled shipping on the Lower Rhine in this period. That means that the forts must have been occupied at least during the shipping season, from March to October (Fulford 2000, 42; Vegetius book IV, 39). From the end of the first century, the function of the forts changed, although the size of the forts stayed roughly the same. This makes it likely that the size of the army also stayed the same.
Only the fort Vechten was almost certainly larger. Indications for this exist especially for the period after A.D. 70 (Polak & Wynia 1991; Zandstra & Polak 2012). It is almost certain that the cohors I Flavia Hispanorum equitata (480 infantry plus 120 cavalry) was stationed there. There are some signs that possibly somewhere in the same period cohors II Brittonum equitata milliaria (800 infantry plus 240 cavalry) was associated with the fort. After A.D. 125, the ala I Thracum (500 men cavalry) was probably stationed in Vechten for a while. It is interesting to note that the occupation of the fort at Vechten consisted at least partly of cavalry units, because it is generally assumed that most of the forts in the Rhine delta were occupied by infantry units.
When we include Katwijk and Bodegraven, there were ten forts between Vechten and Katwijk (fig. 1). Based on an occupation of a maximum of 1 cohors, circa 480 men, per fort and possibly double that number for Vechten, the maximum size of the delta army is estimated around 5000 men.
It is generally assumed that from the late first century onward, it was mainly auxiliary units that were stationed in the forts. The finds of military diplomas indicate that the army units were not local (Polak 2009; idem in press). Less is known about the composition of the army between circa A.D. 40 and the mid-80s. Tacitus’ mention that the Batavians were not allowed to be stationed in their own territory anymore after the revolt in A.D. 69 has led to the assumption that the auxiliary forts in the Lower Rhine delta were largely manned with local soldiers. However, there is no epigraphic evidence for this, although it is known that a large part of the Batavian and Cananefatian auxiliary units were stationed in Great Britain, for example, in the 40s and 50s (De Weerd 2006). Taking these considerations into account, it is likely that the size and composition of the army in the period from A.D. 40 to the mid-80s was similar to that of the following period.
However, there is a large difference in the size of the consuming population till circa A.D. 70 in comparison with the end of the first century onwards. As has been described above, most vici, except those at Vechten and temporarily at De Meern, date after A.D. 70. The civilian settlements that arose around the forts had a military status and were inhabited by people related to the army (Sommer 1984; idem 1991): craftsmen, traders and family members of the soldiers. Although little is known about the size of the population of the vici near the forts in the Rhine delta, this is likely to have been similar to that elsewhere in Europe. That means that in later times the number of people living in the vicus was more or less equal to that of the garrison in the adjacent fort. The composition of the vicus population is a different story. While the people stationed in the forts were mostly men, men as well as women and children lived in the vici.
In short, the consuming population in the Lower Rhine delta from circa A.D. 40 until the end of the first century probably consisted of around 5000 soldiers and 500 to 1000 civilians, comprising men, women and children. It is possible that the number of consumers nearly doubled in the late first century to around 5000 soldiers and as many vicus inhabitants. Considering the presence of cavalry units, especially in Vechten but perhaps also small units in other forts, it is likely that horses, which may have required extra feeding, were kept in the forts.