`And thus," wrote Edward Gibbon in The Decline and Fall of the Roman Empire, "the splendid days of Augustus and Trajan were eclipsed by a cloud of ignorance, and the barbarians subverted the laws and palaces of Rome."
He was coming towards the end of his theme, a consuming passion for more than 20 years. The last page was written 214 years ago today.
Meteorologists browsing through Gibbon's book have noted from time to time that the northward spread of Roman culture coincided with an amelioration of the climate about 500BC.
Indeed, they can be even more precise: they point out that throughout its history, the northern limits of the Roman Empire coincide closely with the 2.8 degrees isotherm for January. In other words, the Romans never ventured anywhere if the average temperature in January was less than 2.8 degrees.
Although he does not put a number on it, Gibbon's conjectures as to why the Romans stopped at Hadrian's Wall - and perhaps why they never crossed the Irish Sea - agree. "The masters of the fairest and most wealthy climates of the globe turned with contempt from the gloomy hills assailed by winter tempests, from lakes concealed in a blue mist, and from cold and lonely heaths over which the forest deer were chased by naked savages."
By the end of the fourth century, however, Europe's climate had begun to deteriorate again and a very severe winter in AD406 gave an unexpected advantage to the Romans' enemies.
As Gibbon points out: "Cold, poverty and a life of danger and fatigue fortify the strength and courage of barbarians. In every age they have oppressed polite and peaceful nations who neglected to counterbalance these natural powers by the resources of military art".
Moreover, that same year, for the first time in centuries, the Rhine froze; the Romans still controlled the bridges and crossing points along the river, but the ice gave the advancing Vandals unimpeded passage westwards, and there before them lay the road to Rome.
Be that as it may, Gibbon had mixed feelings as he penned the last full stop. "I will not dissemble," he wrote afterwards, "the first emotions of joy on the recovery of my freedom. But my pride was soon humbled, and a sober melancholy spread over my mind by the idea that I had taken everlasting leave of an old and agreeable companion, and that whatsoever might be the future fate of my History, the life of the historian must be precarious and short."