The development of the legions 662-679 AUC
Across this period the army continued to evolve in terms of size, doctrine and, to a lesser extent, structure. At the end of the Civil War there were 14 legions deployed from west to east as:
Spain – 1 legion; Gaul – 3 legions; Italy – 3 legions; The Danube – 3 legions; Greece – 2 legions; and, Asia Minor – 2 legions.
This deployment was less in terms of strategy (except the Danubian force) and more a product of the campaigns waged to destroy the rebellion. However there were two major problems with this notionally powerful force. Firstly about 35% of the cohorts now owed their allegiance to an individual not the state. If Catulus' defeat had, for now, removed the threat of renewed civil war, the steady growth of private armies indicated that the next general to rebel might bring one or more legions to his cause rather than a disparate collection of city militias [1]. The second problem was that this force of notionally 257,000 men actually only contained an effective army of 160,000.
The result was the Senate decided to reduce the notional size back to 10 legions and use the released manpower to rebuild this core force. Those disbanded were paid off and often settled in new veterans colonies as Roman rule was consolidated on the rebellious Danubian frontier [2].
The end of this process was the notional army was shrunk to just over 220,000 (11 legions of 18 cohorts) and the effective army was some 50,000 less than this complement.
(this is just after another round of disbanding – hence the small surplus)
By the time of the Third Numidian War (676 AUC), the army had been reduced to 8 legions (150,000 effectives) and a small manpower reserve created. The subsequent development of the legions after that war will be covered in chapter three.
In terms of tactics, this was a period of slow developments, primarily in terms of siege works and the layout of legionary camps.
Equally the discipline and organisation of the heavy infantry remained a focus of tactical developments.
Towards the end of this period, reflecting experience in the Numidian Wars, more and more attention was paid to the tactics and equipment of the cavalry. With the expectation of war with the Eastern powers, cavalry became an increasingly important part of the Republic's armies [3]
Beyond this, the organisation within the legions changed. The preferred strength was 18 cohorts (18,000 effectives) and by 675 these were built around a core of 6-8 heavy infantry cohorts. Increasingly archers, skirmishers and cavalry were integrated into the legions to create mixed forces capable of meeting most foes.
Those legions expected to fight in North Africa often had additional cavalry and the Danubian legions relied more on light infantry support. Although the legions did not have the fixed locations they took under the Principate, nonetheless they started to adjust their structure to the terrain and type of foes they expected to face.
[1] – I believe this is called foreshadowing.
[2] – I sent a lot of the very low manpower 'loyal' cohorts off into the wilds of the Danube where for some unfortunate reason they were destroyed – at least this helped me recovering a manpower reserve as well as restructuring the legions as I wanted them.
[3] – a tiny bit more foreshadowing.