Somewhere in the tropics, a volcanoexploded violently during the year 1258, producing amassive stratospheric aerosol veil that eventuallyblanketed the globe. Arctic and Antarctic ice coressuggest that this was the world's largest volcaniceruption of the past millennium. According tocontemporary chronicles, the stratospheric dry fogpossibly manifested itself in Europe as a persistentlycloudy aspect of the sky and also through anapparently total darkening of the eclipsed Moon. Basedon a sudden temperature drop for several months inEngland, the eruption's initiation date can beinferred to have been probably January 1258. Thefrequent cold and rain that year led to severe cropdamage and famine throughout much of Europe.Pestilence repeatedly broke out in 1258 and 1259; itoccurred also in the Middle East, reportedly there asplague. Another very cold winter followed in1260–1261. The troubled period's wars, famines,pestilences, and earthquakes appear to havecontributed in part to the rise of the Europeanflagellant movement of 1260, one of the most bizarresocial phenomena of the Middle Ages. Analogies can bedrawn with the climatic aftereffects and Europeansocial unrest following another great tropicaleruption, Tambora in 1815. Some generalizations aboutthe climatic impacts of tropical eruptions are madefrom these and other data.