On Oct. 11, 1138, the ground under the Syrian city of Aleppo began to shake. The city sits on the confluence of the Arabian and African plates, making it prone to temblors, but this one was particularly violent.

The magnitude of the quake is lost to time, but contemporary chroniclers reported that the city’s citadel collapsed and houses crumbled across Aleppo. The resulting death toll is estimated at around 230,000, but that figure comes from the 15th century, and the historian who reported it may have conflated the Aleppo quake with one that occurred in what is now the modern-day Eurasian country of Georgia, according to a 2004 paper in the journal Annals of Geophysics(opens in new tab).