This episode takes place from 23 to 29 AD.
Although now known only as Caligula he was more properly named Gaius Julius Caesar Augustus Germanicus. He earned the nickname Caligula as a child travelling with his father's legion in Germania. Reportedly the soldiers made him a little uniform, complete with soldierly boots known as caliga, and he soon earned the nickname Caligula meaning "little boot". It was a nickname he grew to hate as he aged and was not something any wise person used in his earshot.
Kevin Stoney reprised his role as Thrasyllus of Mendes from The Caesars (1968), which also covered the reigns of the first four Roman Emperors.