Climatic conditions in the Alps in the years about the year of Hannibal's crossing (218 BC)

Hannibal and his force (troops, pack animals and elephants) crossed the Alps from France to Italy in the autumn of 218 BC. An examination of treering density and glacier data for the Alps indicates that the year of crossing fell into a period when temperature conditions were much the same and, perhaps, slightly milder than those of the current century since about 1920 - a perid of almost worldwide warming. Absolutely dated tree-ring data for southern Central Europe corroborate that the growing periods of 218 BC and neighboring years were mild.As to the autumn month when the crossing was accomplished, temperature conditions favor the month of September. In the area of the passes, one of which was selected by Hannibal for the traversal at the approximate altitudes of 2000–2500 m MSL, the temperatures are, in the mean below freezing from about mid-October. The ancient historians (Polybius, Livy and others) do not mention frosbite casualties. Below-freezing temperatures would have seriously affected troops coming from North Africa and southern Spain. Presumably, temperatures were above freezing during the ascent phase and the rest of two days on the pass.By the 3rd century BC the Alpine glaciers were in a backward position compared with their position in 900-350 BC. This fact and the mildness of the climate, inferred from tree-ring analyses, suggest that ice conditions were not severe in the Alps in 218 BC.The author has been visiting with the Department of Meteorology, University of Copenhagen, since 1986.