Climate of ancient Rome

In the first half of the 1st millennium BC, the climate of Italy was more humid and cool than now and the presently arid south saw more precipitation.

[1] During the annual melt of the mountain snow, even small rivers would overflow, swamping the terrain (Tuscany and the Pontine Marshes were deemed impassable in antiquity).

[2] The written, archaeological and natural-scientific proxy evidence independently but consistently shows that during the period of the Roman Empire's maximum expansion and final crisis, the climate underwent changes.

[8] Evidence for a cooler Mediterranean climate in 600 BC–100 BC comes from remains of ancient harbors at Naples and in the Adriatic which are located about one meter below current water level.

Edward Gibbon, citing ancient sources, thought that the Rhine and the Danube were frequently frozen, facilitating the invasion of barbarian armies into the Empire "over a vast and solid bridge of ice".

[10] The biotopes of Heterogaster urticae, which in Roman times occurred farther north than in the 1950s, suggest that in the early Empire mean July temperatures were at least 1 °C above those of the mid-20th-century.

[8] A comparison of modern wind roses with the situation in the 1st century AD shows some differences: in that time northern inflows in winter were quite rare.

[15] According to Rhoads Murphey, the total yearly grain supply from North Africa to Rome, "estimated as enough to feed about 350,000 people, is by no means impossible to produce for export under present conditions".

[18] In 61 AD Seneca the Younger described the high level of air pollution in Rome, which was associated with the extensive wood burning for fuel.

[3] Dendrochronology indicates that severe drought which began in 338 and persisted until 377 forced the nomadic pastoral federation of Huns to seek pastures and predation farther to the west and south.