In 400AD, more than 700,000 people lived in Rome, a city of 28 libraries, 856 public baths and 47,000 apartment blocks. It was the greatest city on Earth, the jewel of an empire that controlled the lives of a quarter of the planet’s population. And yet, within decades this astonishingly successful empire had crumbled and a mere 20,000 lived in Rome.

Historians have long been fascinated by “the single greatest regression in all of human history”. Using data from “natural archives” such as ice cores and genomic evidence, Harper offers a compelling new take on Rome’s fate, arguing that it was “the triumph of nature over human ambitions”.

Pandemics and natural changes in the climate caused by volcanic eruptions sent Italy reeling backwards. Infectious diseases such as smallpox spread rapidly through the urbanised empire thanks partly to its famed roads. AD536-45 was “the coldest decade of the last 2,000 years”, causing food shortages. Plague, climate change and war reversed a millennium of material advances.

A work of remarkable erudition and synthesis, Harper’s timely study offers a chilling warning from history of “the awesome, uncanny power of nature”.

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