History of the Roman Empire from this point on, leading his biographers to label him as insane. Most of what history remembers of Caligula comes from Suetonius, in his book "Lives of the Twelve Caesars". According to Suetonius, Caligula once planned to appoint his favourite horse Incitatus to the Roman Senate. He ordered his soldiers to invade Britain to fight the Sea God Neptune, but changed his mind at the last minute and had them pick sea shells on the northern end of France instead. It is believed he carried on incestuous relations with his three sisters: Julia Livilla, Drusilla and Agrippina the Younger. He
Holy Roman Emperor the inheritors of the title of Emperor of the Western Roman Empire, despite the continued existence of the Eastern Roman Empire. In German-language historiography, the term "Römisch-deutscher Kaiser" ("Roman-German emperor") is used to distinguish the title from that of Roman Emperor on one hand, and that of German Emperor ("Deutscher Kaiser") on the other. The English term "Holy Roman Emperor" is a modern shorthand for "emperor of the Holy Roman Empire" not corresponding to the historical style or title, i.e., the adjective "holy" is not intended as modifying "emperor"; the English term "Holy Roman Emperor" gains currency in the interbellum