Economic factors, to the extent that they were favourable, played an obvious part in promoting both cultural and political unity. So far as acculturation was concerned, a limit to its achievement was clearly set by the amount of disposable capital among non-Romanized populations. The cost of such luxuries as schooling in Latin or frescoes on one’s walls were high. But more and more people could afford them as the benefits of Roman occupation were spreading. The rising levels of prosperity did not, however, result from a special benevolence on the part of the conquerors, intent as they were (and often cruelly intent) on the pleasures and profits of physical mastery over the conquered. Rather, they can be explained, first, by the imposition of the Pax Romana, which gave urban centres surer access to the surrounding rural areas and rural producers access in turn to convenient, centralized markets; second, by the sheer attractiveness of imported articles, which intensified efforts to increase the power to buy them; third, by the economic stimulation afforded by taxes, which had to be paid on new earnings but which remained in the provinces where they were raised. In the fourth place, prosperity also rose in the regions least Romanized. This can be explained by the fact that they tended to be heavily garrisoned and the soldiers spent their wages locally. So far as they could, they bought goods and services of a Roman sort and generally attracted concentrations of people likely to develop into cities of a Roman sort. The economic impact of army payrolls was all the greater because of the cash added to them from taxes raised in other, more developed provinces in the East. Much of the urbanization and enrichment of the western and northern provinces can be explained by these four factors.
Until the 1950s or ’60s the sources for studying the economy of the empire were insufficient. The archaeological sources were too scarce and heterogeneous to be of much help, and the written ones contained barely usable amounts of quantified data; economic analysis without quantification, however, is almost a contradiction in terms. Thus discussion was obliged to limit itself to rather general remarks about the obviously wide exchange of goods, the most famous points of production or sale of given articles, techniques of banking, or commercial law. This is still the case with regard to the Eastern half of the Mediterranean world, where excavation has made relatively little headway; but, for the West, archaeological data have greatly increased in recent decades in both quantity and intelligibility. As a result, a growing number of significant statements based on quantification can now be made. They are of special value because they bear on what was economically most important—namely, agriculture. Like any preindustrial economy, that of the empire derived the overwhelming bulk of its gross national product from food production. One would therefore like to know what regions in what periods produced what rough percentage of the chief comestibles—wine, oil, wheat, garum or legumes. Thanks to techniques such as neutron activation analysis or X-ray fluorescence spectrometry, the contents of large samples of amphorae at certain market junctures can be identified, dated by shape of vessel, and occasionally ascribed to certain named producers of the vessel, and the information drawn into a graph; or, the numbers and find-spots of datable fine “china” (so-called Arretine ware or later equivalents) or ceramic oil lamps from named producers can be indicated on a map of, say, Spain or France. The yield of such data underlies statements made above regarding, for example, the supersession of Italy as producer of several essential agricultural products by the mid-1st century ad, the concurrent transformation of Gaul from importer to exporter, and the emergence by the 3rd century of northern Africa as a major exporter of certain very common articles. Information of this general nature provides some sense of the shift in prosperity in the Western provinces.
In the age of the Antonines, Rome’s empire enjoyed an obvious and prosperous tranquility; modern consensus has even settled on about ad 160 as the peak of Roman civilization. Whatever measurement may be used in this identification, however, an economic one does not fit very well. Evidence, as it accumulates in more quantifiable form, does not seem to show any perceptible economic decline in the empire as a whole after roughly 160. Rather, Italy had probably suffered some decrease in disposable wealth in the earlier 1st century. Gaul’s greatest city, Lugdunum, had begun to shrink toward the end of the 2nd, and various other regions in the West suffered setbacks at various times, while all of Greece continued to be poor. Other regions, however, had more wealth to spend, and as is manifest in major urban projects of utility and beautification or in the larger rooms and increasingly expensive decoration of rural villas. Roman rule also brought extraordinary benefits to the economies of Numidia and Britain, to name its two most obvious successes.
To the extent the empire grew richer, modern observers are likely to look for an explanation in technology. As noted above, in Augustus’ reign a new mode of glassblowing spread rapidly from Syria to other production centres; Syria in the 3rd century was also the home of new and more complicated weave patterns. Such rather minor items, however, only show that technical improvements in industry were few and insignificant. The screw press for wine and olive oil was more efficient than the levered variety, but it was not widely adopted, even within Italy. Waterwheels for power, known in Anatolia in Augustus’ reign, were little used; a few examples in Gaul belong only to the later empire. Similarly, the mechanical reaper was found only in Gaul of the 4th century. Perhaps the most significant advances were registered in the selective breeding of strains of grains and domestic animals: for example, the “Roman” sheep (which had originated in the Greek East) spread throughout Europe, banishing the inferior Iron Age species to a merited exile in the Outer Hebrides (the Soay sheep of St. Kilda island). What is vastly more significant, however, than these oddments of technological history is the minute subdivision of productive skills and their transmission from father to son in populations adequate to the demand—for iron ore from Noricum, most notably, or for glass and paper from Alexandria. Specialization in inherited skills produced a remarkably high level of proficiency, requiring only the security of the Pax Romana for the spreading of its products everywhere—transport itself being one of those skills.
The health of the economy no doubt helps to explain the political success of the empire, which was not disturbed by frequent revolts or endemic rural or urban unrest. On the other hand, there were limits in the economy, which expressed themselves through resistance to taxation. Tax levels settled at the enforceable maximum; but revenue fell far short of what one might expect, given the best estimates of the empire’s gross national product. The basic problem was the tiny size of the imperial government and the resulting inefficiency of its processes. Moreover, it could not make good its inadequacies by borrowing in times of special need; Nero’s need to harry his millionaire subjects with false charges of treason in order to pay for his incredibly expensive court and spendthrift impulses reflects the realities of raising revenue. So do the very cautious experiments of Augustus in setting army pay and army size. Ultimately, the military strength of the empire was insufficient—inadequate for emergencies—because of these realities. The army