What happens when the people of a great nation gradually realize that their leader may not be, er, quite right in the head?

When Caligula became Roman emperor in A.D. 37, the people rejoiced. “On all sides, you could see nothing but altars and sacrifices, men and women decked in their holiday best and smiling,” according to the first-century writer Philo.

The Senate embraced him, and he was hailed as a breath of fresh air after the dourness, absenteeism and miserliness of his great-uncle, Emperor Tiberius. Caligula was colorful and flamboyant, offering plenty of opportunities for ribald gossip. Caligula had four wives in rapid succession, and he was said to be sleeping with his sister. (Roman historians despised him, so some of the gossip should be treated skeptically.)

He was charming, impetuous and energetic, sleeping only three hours a night, and he displayed a common touch as he constantly engaged with the public. His early months as emperor brimmed with hope.