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
Frederick I, Holy Roman Emperor from the donkey. To add to this debasement, they were made to announce, ""Ecco la fica"" (meaning "behold the fig"), with the feces still in their mouths. It used to be said that the insulting gesture, (called fico), of holding one's fist with the thumb in between the middle and forefinger came by its origin from this event. Frederick's first marriage, to Adelheid of Vohburg, did not produce any children and was annulled. From his second marriage, to Beatrice of Burgundy, he had the following children: Frederick I, Holy Roman Emperor Frederick I (, ; 1122 – 10 June 1190),