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Claudian Army Reforms

Claudian Army Reforms: modern name of a wide-ranging series of changes of the Roman military, initiated early during the reign of the emperor Claudius (41-54).

The Roman army was, essentially, created by Julius Caesar, whose legions, although meant to be temporary, became permanent units, surviving their founder. Marc Antony and Augustus used them, and the latter handed them over to Tiberius. When he died, several legions were more than ninety years old. They had long traditions, and Augustus and Tiberius had not changed much, although the terms of service, payment, and pension had become standardized. The grand strategy -whether this was conscious or not- had not changed either: the Empire consisted of a nucleus of provinces, surrounded by a periphery of vassal states, which would one day be converted into provinces; at that moment, a new periphery of vassal states would be created, which in turn would one day be annexed. 

This conservatism came to an end during the reign of Claudius. He inherited Caligula's plan to conquer Britain and must, during his first regnal years, have dedicated much time to military planning. He was more or less forced to: after all, he had come to power against the wishes of the Senate, could not present himself as a member of the imperial family (the gens Julia), and needed to show that he was worthy of his new position. He had, on the one hand, to break with the traditions associated with his predecessors, while he had, on the other hand, to show that the Roman armies would be just as efficient. So, he had reasons to listen to generals and officers who proposed military innovations, and decided to conquer Britain.

As we will see in our discussion of the raising of new legions, reform may have started during Caligula. It is certainly possible that the accession of Claudius, a non-military man who needed military support, offered an opportunity to the reformers.


The main military decision by Claudius was, of course, the conquest of Britain, for which new legions were necessary. It has long been recognized that the legions XV Primigenia and XXII Primigenia were raised between 37 and 43. Both Caligula and Claudius had reasons to form them, because both had plans to invade Britain. Primigenia was one of the titles of Fortuna, the favorite goddess of Caligula and his father Germanicus; it may well have been a personal favorite of Claudius as well, but this is not indicated in our sources. Because a connection between Fortuna and Claudius is merely hypothetical, while this connection certainly connects between Caligula and this deity, the logical principle known as Ockham's Razor forces us to conclude that it is more likely that Caligula was the founder of these units.

Elsewhere, however, Claudius preferred a defensive strategy (and perhaps the conquest of Britain, which meant that the Ocean became Rome's frontier, was meant to be defensive too). Along the Rhine, the first evidence for stone foundations of Roman fortresses (and, hence, the intention not to move across the Rhine), is from Xanten. Between the forts, watchtowers were built, like the one at Leidsche Rijn, which can be dated to the forties. In Raetia, units were transferred to the Upper Danube (and to supply them, the Via Claudia was built), while Thrace was annexed, creating better access to the forts along the Lower Danube. In other words, it seems that Claudius created the limes along the Rhine and Danube. We would like to know more about it, but it is interesting to read how general Corbulo was recalled when he tried to subdue the Frisians, who lived across the Rhine (Tacitus, Annals, 11.19).

At Cologne, the fleet (Classis Germanica) received a base at Alteburg and was reorganized. The Classis Britannica was created, and the command structure of the two Mediterranean navies were changed: from now on, they had the rank of procurator Augusti et praefectus classis, a remarkable title that combines a civil and a military rank.


Until Claudius, there had been little system in the career path of Roman knights serving in the army. According to Suetonius, the order of promotion was praefectus cohortis - praefectus alae - tribunus militum (Claudius, 25.1). This was was not a long-lived reform: when Nero was emperor, the sequence had become praefectus cohortis - tribunus militum - praefectus alae. This last office was, from now on, reserved to equestrians only.

Diploma of an Isaurian soldier named Lualis, from Weissenburg (Germany)
Diploma of an Isaurian soldier named Lualis, from Weissenburg (Germany)
The auxiliary troops appear to have been reorganized as well. Until Claudius' reign, their cohortes and alae were usually temporary units, mostly named after a commander or a tribe. Claudius created permanent units with names that consisted of a number and an ethnic name, like Ala I Sebastenorum. Terms of service were also fixed: any auxiliary soldier was entitled to Roman citizenship. The evidence for this development consists, of course, of countless numbers of diploma's.

Other changes

During the reign of Augustus and Tiberius, the walls of fortresses and forts often followed the contours of the land, although some attempt was made to keep it as rectangular as possible (e.g., Anreppen). After Claudius, we see the rise of camps and forts with increasingly square shapes.

There may have been a change in tactics as well, because old swords of the Mainz type were replaced with the Pompeii type. The first one is useful for a soldier who is thrusting with the point of his weapon during a formal battle; the second one has a shorter point and may allow for other types of fight. The changeover can not be dated precisely, but appears to have been well underway in the mid-first century.

Finally, armor may have changed. The bronze Coolus (or Hagenau) type was replaced with the Imperial-Gallic (or Weisenau) type, which was usually made of iron and offered better protection of the neck. The old chain mail or lorica hamata remained in use, but the lorica segmentata, the modern name of an assembly of metal plates, may have become more popular in this age. But this is not very certain. Fragments of this type of armor have been found on earlier sites (Dangstetten, Kalkriese), so the change may, after all, be apparent only.


The main article on the subject is C. Thomas, "Claudius and the Roman Army Reforms", in: Historia 53 (2004); this webpage is essentially a summary, with some modifications and changes in emphasis. Other literature:

This page was created in 2009; last modified on 30 January 2015.