Recent sources say that Caligula probably had encephalitis. Ancient sources, like Roman biographers Suetonius and Cassius Dio, describe Caligula having a "brain fever". The symptoms of Caligula's condition as well can be attributed to an attack of meningitis.

What was Caligula illness?

But assuming the much-maligned emperor was the loon his chroniclers describe, some scholars have suggested that an illness made him come unhinged—possibly temporal lobe epilepsy, hyperthyroidism or Wilson's disease, an inherited disorder that can cause mental instability.

What made Caligula insane?

There are few surviving sources about the reign of Caligula, though he is described as a noble and moderate emperor during the first six months of his rule. After this, the sources focus upon his cruelty, sadism, extravagance, and sexual perversion, presenting him as an insane tyrant.