After blazing a trail across two continents to reach central Europe in 1242, the Mongol army led by Genghis Khan’s grandson suddenly and mysteriously stopped and retreated. Although many explanations have been proposed for this reversal, ranging from internal politics to mounting casualties, the real reason may have been simply that a cold, wet winter meant there was not enough grass to feed their horses, New Scientist reports. After analyzing tree rings from the area of modern-day Hungary, scientists found that the winter of 1242 likely produced a lot of snow that would have flooded the region in the spring, according to a study published last week in the journal Scientific Reports. These swamplike conditions could have forced the Mongols to turn back to find grasses in Russia.
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