Why did the Roman Empire collapse? Kyle Harper’s very readable book The Fate of Rome makes a persuasive case that this was much to do with climate change and epidemic disease, both of which were consequences of the process of Empire itself.

It is salutary to reflect that such a political system is a process that has consequences on its environment and its citizens and their well-being. The parallels with today’s climate change and threatening global pandemic are obvious.

We could see this fatalistically in cataclysmic terms, or we can see it optimistically as being a story in need of constant renewal and redirection. It’s our choice.

My notes below outline the Empire’s story.

In the early years of empire, from Augustus Caesar in 27BC to Marcus Aurelius 161-180 was a sequence of reasonably stable and long-lived Emperors, the later years characterised by Gibbon as the ‘happiest era’. This just happened to coincide with a particularly benign period of Mediterranean climate, known as the Roman Climate Optimum (RCO).

After this, the climate became more variable, drier and colder. Deforestation was probably a significant cause. The expansion of Empire and consequent trading routes also made the Empire more vulnerable to diseases. The Antonine Plague 165-180 may have killed one third of the population.

The Empire survived these consequences of its own growth, but life was never quite the same again. It certainly continued to develop. In 212 Caracalla granted citizenship to all inhabitants of the Empire, which effectively became a huge state.

The ending of the RCO was accelerated by a period of lower solar activity and occasional failure of the Nile floods, the Empire’s great fertile insurance policy.  In 245-6 the Plague of Cyprian struck another blow, correlating with an explosion of Christianity.

The fourth century was a period of relative calm again. The Empire was centralized and under Constantine a ‘new Rome’ was established at Constantinople, and Christianity became a state religion

Climate change affected not only Europe, but the Steppes, the vast area of grass, scrub-land and desert between Hungary and China. The people who became known as the Huns were fearsome horseback fighters who appeared in Europe around 370. The two sides of Empire became split, and the Western Empire fell to a combination of Goths/Huns. The Huns eventually retreated as they could not cope with the diseases of the Mediterranean, but the Western empire was no more.

The Eastern Empire remained, and by the 6th century Constantinople was a global trading hub. From 527-565 Justinian led another period of renewal, including the building of Hagia Sophia. But in 541 the rodent flea-borne plague arrived, along with the host black rat – just after years of exceptional volcanic activity which led to years of subdued summers. The so-called Justinian Plague lasted on and off for 200 years.

The Late Antique Little Ice Age now completed the job of emasculating the Empire. Heraclius 610-41 presided over its failure. The eastern provinces were dismantled by the emerging energies of Islam, and only a rump Byzantine state remained.