10 of the worst Roman Emperors in history.

4  Carcalla

Caracalla was not insane. He was malicious and sadistic. From 211 to 217 he presided over an awe-inspiring spectacle of fearsome acts. He had his brother and co-emperor, Geta, and Geta’s wife, assassinated.
The citizens of Alexandria, Egypt ridiculed this crime with a public play, and when Caracalla got wind of it, he traveled with an army to Alexandria, invited the citizens into their city square, and slaughtered them, looting and burning the whole city. 20,000 died.
This was the sort of emperor he showed himself to be in almost every Roman province at that time, putting down all hints of rebellions, even where rebellions were not imminent. At the slightest whiff of discord, he ordered death. Wherever he went, his army killed, raped, and destroyed.
He was murdered by one of his Guardsmen, on April 8, 217, while urinating on the side of the road outside Carrhae. Caracalla had had the Guard’s brother executed on a false accusation.