Economics of the Roman army
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The economics of the Roman army concerns the costs of maintaining the Imperial Roman army and the infrastructure to support it, as well as the economic development to which the presence of long-term military bases contributed. Supply contracts with the military generated trade with producers near the base, throughout the province, and across provincial borders.
The size and growth of the Roman army of the Principate may be summarised as follows:
Note: Figures are based on official (not actual) unit strengths and exclude Roman navy effectives and barbarian foederati.
In addition, the Roman navy contained probably 30,000–40,000 marines, sailors and oarsmen, of which 15,000–20,000 in the Mediterranean fleets at Misenum and Ravenna (contrary to popular belief, Roman warships of this period were not rowed by the forced labour of convicts or slaves, but by volunteer professional oarsmen) and perhaps the same again in the classis Britannica (English Channel fleet) and the fluvial flotillas on the Rhine and Danube.
Furthermore, substantial numbers of irregular barbarian troops (foederati) were in the paid service of the empire during the whole period: the number is unknown, but there were at least 5,500 in Britain alone about 175 (surrendered Sarmatian cavalry posted there by Marcus Aurelius). If this figure is multiplied by 10 to represent other frontier provinces, it is possible that there may have been 50,000–60,000 such irregulars at any given time.
At its peak under emperor Septimius Severus (r. 197–211), therefore, the standing Roman military establishment may have comprised over half a million effectives.
This was a very significant burden on the Roman economy, which was pre-industrial: at least 80% of its inhabitants worked in agriculture. Virtually all the taxes and rents raised by the imperial government were spent on the military: about 80% of the imperial budget in c. 150.This military spending constituted, on one estimate, about 2.5% of the empire's GDP, which seems a tolerable burden if compared to the USA, today's global superpower, which spent 3.8% of its GDP on defence in 2006 (18% of the federal budget). But the comparison is misleading. Due to modern technology, a modern economy is far more productive per capita than the Roman economy: on one estimate, the average American in 1998 was at least 73 times more economically productive, in comparable terms (i.e. in international dollars), than a Roman in the 1st century AD. Therefore, taxes (and compulsory services) to support the Roman military would have taken a much greater share of surplus per capita production i.e. surplus to the subsistence needs of producers. For the average peasant, the taxes and services he was obliged to provide to the military would have represented a significant share of his disposable surplus.
There is also a great disparity between the costs of the 4th-century army and its 2nd-century counterpart. The much lower remuneration for 4th-century soldiers is reflected in total army costs. Duncan-Jones estimates the total annual cost of the military in c. 150 AD at c. 670 million sesterces. That translates into 0.67 million aurei or 16,800 pounds of gold. This compares with Elton's estimate of c. 47,000 lbs of gold for a 4th-century military establishment of 450,000. Even if the establishment was the 600,000 estimated by A. H. M. Jones, the cost would still be only about a third that for the 2nd-century army. Such a disparity is difficult to explain. Either the imperial government was collecting far less tax than in the 2nd century (an unlikely possibility, given the numerous complaints about the weight of the tax burden). Or it was spending much more on other sectors. These may still have been "defence-related": e.g. fortifications, irregular foederati forces, or payments to barbarian chiefs to buy peace and allegiance. The latter had a long history: such payments are recorded in Julio-Claudian times.
- aerarium militare, the military treasury at Rome from which veterans' benefits were funded
- donativum, a bonus paid by emperors to secure soldiers' loyalty
- David Mattingly, "The Imperial Economy," in A Companion to the Roman Empire (Blackwell, 2010), p. 296.
- 25 legions of 5,000 men each
- 28 legions of 5,500 each (double-strength 1st cohorts introduced under Domitian (r. 81–96)
- 33 legions of 5,500 each
- Implied by Tacitus Annales IV.5
- P. Holder Auxiliary Deployment in the Reign of Hadrian (2003) 120
- J. C. Spaul ALA (1996) 257–60 and COHORS 2 (2000) 523–7 identify 4 alae and 20-30 cohortes raised in the late 2nd/early 3rd centuries
- Goldsworthy (1995) 58: 9 cohorts of 480 men each plus German bodyguards
- Goldsworthy (1995) 58: 9 double-cohorts of 800 men each plus 2,000 equites singulares
- Implied by Tacitus Annales
- Hassall (2000) 320 estimates 380,000
- MacMullen How Big was the Roman Army? in KLIO (1979) 454 estimates 438,000
- MacMullen (1979) 455
- John Lydus De Mensibus I.47
- Keppie (1996) 383
- Mattingly (2006) 356
- R. Duncan-Jones Money and Government in the Roman empire (1994) 45
- Cf. article by R.W. Goldsmith in Journal of the Int'l Assoc. for Research in Income and Wealth Series 30 (1984) 263–88
- The Economist Pocket World in Figures (2007)
- Derived from historical GDP estimates in A. Madison The World Economy: a Millennial Perspective (2001)
- Duncan-Jones (1994) 45
- Elton (1996) 124