Biology Comics

The Roman Empire

The first conquests of the Roman Empire were in the East and immensely profitable. These old Mediterranean civilizations were rich and could afford much tribute. The profits funded new conquests.

Most of Italy was forested in BC 300. The newly cleared lands yielded large crops. The richness of the Italian soil was another basis of the Empire.

The western lands (Gaul, Spain, England, the Rhineland), which were conquered last, did not pay the costs of conquest. These lands were lightly settled and poor. While their soils were good, the cost of transporting crops like wheat overland was too great.

The Roman economy was overwhelmingly agricultural. Trade and industry were perhaps 10% of the economy. Once the conquests were over (about AD 1) agriculture had to pay the costs of administration.

A smallholder of the early Republic cultivated a hectare by hand with a hoe, growing olives, vines, fruit trees, grains, vegetables, forage crops and animals. The multistory canopy saved labor, reduced erosion, and was twice as productive in foodstuffs as plowing with an ox to grow grain. Some farmers applied manure, human manure, crushed limestone and ashes to their fields and grew cover crops on the grain fields left fallow every other year.

For large landowners plowing with oxen to grow grain was more profitable than hoe agriculture. While good farming practices were known, most large farmers didn’t follow them. In the two field system of the Greeks that was taken over by the Romans, land was plowed three times a year, whether cultivated or fallow, to control weeds. Erosion from plowland near Rome has been estimated at three quarters to four inches per century.

Iron had come into common use in Italy by BC 500 (for shovels, plow points and other tools) and forests were cut to smelt it, to fire pottery and burn brick. Trees were also cut for building material. Eroded soils from forests slid down the hillsides to the valley bottoms. Forests were often grazed after being cut.

As the more wealthy began to dominate Roman society after BC 200, large estates began to replace smallholdings, especially in the countryside around Rome. This landscape, the Campagna, fed the city until about BC 200.

Wheat, oil and wine could be profitably shipped by sea. The conquest of Egypt, with its soils renewed by the Nile, and the new lands of North Africa, let Rome feed itself after AD 1. The Imperial Middle East was completely deforested by AD 100 however and most of its upland soils were degraded by AD 200. Grazing replaced the cultivated grainland, which had replaced the forests. By the end of the Empire the silt carried by the Nile fed Rome. (The same African silt and the new lands of Sicily had also fed the declining Greek states 1000 years before.)

Land itself was taxed. No provision was made for varying yields. The government financed itself on a cash basis. Its single tax was inelastic and made it difficult to raise additional funds in time of need (as in war). Emperors in need of money debased the currency, an indirect tax.


Tenant farmers were taxed too highly to accumulate capital. When crops failed they abandoned their lands and left for Rome, where Egyptian wheat was distributed free to the citizens (the dole).


As more land fell into the hands of the large landowners, erosion increased. As yields fell, taxes became more difficult to pay and more and more land was abandoned. Abandoned land reached a third to a half of some provinces. Tax receipts collapsed. In AD 300 abandoned lands in the Campagna were estimated at 75,000 smallholdings. Taxes were doubled AD 324-364.

Eroded soil turned river valleys into marshlands. Malaria became a problem after AD 200. Malaria increases child mortality and reduces people’s capacity to work. In time, both slopes and valley bottoms were used for pasture rather than cultivated.

With the end of the conquests and the money they brought in, and the declining agricultural yields, and thus declining tax revenues, Rome no longer worked. The population of the Empire never recovered from the plague of the AD 160s. With the barbarian invasions of the AD 200s (crops destroyed, people killed and enslaved, animals killed or stolen), Rome began to go bankrupt. The literacy rate fell, but the size of the army and bureaucracy increased. The army was more and more staffed by barbarians.

As large estates further consolidated (city magistrates, whose position had become hereditary, had to pay the cost of city services), and plowed lands increased, yields fell further, and the countryside grew emptier. It now took ten times the land to feed a Roman than in the days of the early Republic. (Five hundred years of erosion would have reduced topsoil in the Campagna by 4 to 20 inches, and more on sloping lands.) Laws tied tenants to the land to prevent them from abandoning it. What the land needed to become productive was known; perhaps the larger structural problems of the Empire were also known. The western provinces were let go AD 260-274. By the late 300s, the Romans waited—as the poet Cavafy said—for the barbarians to deliver them from the Empire.



(In this essay I am indebted to The Collapse of Complex Societies by Joseph Tainter and Dirt by David Montgomery.)