In 1937, the Italian massacre of Yekatit 12 took place, in which as many as 30,000 civilians were killed and many others imprisoned. This massacre was a reprisal for the attempted assassination of Rodolfo Graziani, the viceroy of Italian East Africa. The Italians employed the use of asphyxiating chemical weapons in their Ethiopian invasion. The Italians regularly dropped bombs throughout Ethiopia that carried mustard gas and debilitated the Ethiopian forces. On the whole, the Italians dropped about 300 tons of mustard gas as well as thousands of other artillery. This use of chemical weapons amounted to egregious war crimes.