Background: Chinggis Khaan's (Ghengis Khan) Great Mongol Empire, centered on the Orkhon Valley, was the largest land empire in world history. At the time of Chinggis' death, the empire stretched from the Pacific Ocean to the Caspian Sea and northern Persia (Fig 1). The empire continued to expand such that Mongolians controlled or influenced areas from the Hungarian grasslands to Vietnam, Syria, Bagdad and Japan by the end of the 1200s. The extent of the Mongol Empire and the range of landscapes and cultures that fell under this empire are unrivaled. The impact of Chinggis Khaan's adaptive, merit-based leadership still influences today's world (Weatherford, 2004) and that he was one of the world's greatest leaders.

Figure 1 - The Mongol Empire (shaded portion of Eurasia) at 1227 CE, the time of Chinggis Khaan's death.

Questions still linger, however, as to how nomadic tribes from cold, arid Mongolia could conquer the agricultural societies of China and eastern Europe: "Did a favorable climate provide an energetic base conducive to Mongolian expansion?" Also, "Did a deteriorating climate lead to Mongol contraction?" Until now, no drought data existed to help address these questions.

Following our serendipitous discovery of ancient, subfossil wood from near the Orkhon Valley, we now have the first opportunity to answer these questions through the development of an annually-resolved, drought record covering the Common Era (CE). Despite having had the time to only sample 17 Siberian pine (Pinus sibirica), including just 7 subfossil samples, our record dates to back 658 CE. Because we were investigating fire history, we sampled only ~2 km2 in <4 hrs. Ultimately, the new record will allow for the creation a complete context of annual climatic in the rise and fall of the Mongol Empire with the use an existing TRL temperature record in central Mongolia (D'arrigo et al., 2001).

Historians have suggested that variable climate and drought drove the Mongol armies to raid eastern European farmers (Lattimore, 1938) - our preliminary results directly contradict this speculation. Rather, it appears that climatic conditions ideal for grassland productivity coincided with expansion of the Mongolian Empire. Data collected through this proposal will allow us to test the hypothesis that a climatic optimum led to high grassland productivity and aided Mongol expansion.