In 1242, Hungary was poised on the edge of disaster: The Mongols, who already conquered large swaths of Asia and Eurasia (including China and Russia), had set their sights on Eastern Europe, and Hungary was the next target.
Hungary was ill-prepared, and in the spring of 1241, an army of around 130,000 Mongol soldiers invaded, devastating the eastern portion of the country, destroying the capital city, and causing the king of Hungary, Béla IV, to flee to Austria. In the winter of 1242, the invasion into the western half began, leaving mass destruction in its wake—but then suddenly, seemingly out of nowhere, the Mongols withdrew and returned to Russia, never to return again.
No explanation was ever given to the surprising move, leaving historical scholars puzzled for hundreds of years. Numerous ideas have been offered up, though. Was the retreat a result of political upheaval caused by the death of one of Genghis Khan’s sons, Ögödei Khan, in December of 1241? Did the Eastern Europeans put up more of a fight than they were expecting? Nothing seemed to fit quite right.
Finding the solution to an ancient problem
Until now that is, as a pair of researchers from the Swiss Federal Research Institute and the Institute for Advanced Study in the U.S., Ulf Büntgen and Nicola Di Cosmo, believe they may have finally found the solution: plain old bad weather.
According to their paper in Scientific Reports, the team made use of historical records and tree ring data in Hungary to determine the conditions at the time of the invasion. Tree rings, whose patterns are affected by the weather, are very specific in terms of dates—and so data on the rings can provide a screenshot of the weather for different seasons of each year. In this case, the tree ring data suggests that the winter of 1242 was particularly bad—which is also corroborated by the historical documents.
However, that winter wasn’t bad because it was extremely cold or snowy, but because the temperature was just low enough to cause widespread freezing across Hungary. When the spring of 1242 arrived, everything melted, leading to flooding. And, as it turns out, the part of Hungary the Mongols were looking to invade sits at low elevations, meaning all the meltwater puddled across the land. Because of this, the region was quickly filled with mud (obviously making traveling a challenge), which kept the grasses across the region from growing.
Why is a lack of grass such a huge problem? Well, quite simply, the Mongols invaded on horseback, with each cavalryman owning three or four apiece. The horses survived by eating grass, and with the land quickly becoming a mud pit, it could no longer sustain the Mongols’ horses.
Or in short, it seems that the weather conditions were just right to make an invasion a tactical challenge, and that the Mongols simply decided it was not worth the trouble.
Image credit: J. Paul Getty Museum