According to the German editor, Heribert Prantl, Caligula showed his madness by appointing a goat to the Roman Senate. His successor burnt all his decrees and order.
The Madness of Caligula
http://www.ancient-origins.net/history-famous-people/madness-caligula-002132
The story of Caligula is a legacy that goes back thousands of years. In his short life of only 29 years he experienced horrific tragedy, a deep hatred for the man who killed his family, great power as the Emperor of Rome, and eventually, a brutal death. While his reign as Emperor lasted only a few short years, the stories of Caligula have lived on for millennia, his name becoming synonymous with murder and debauchery. In the latter years of his life, his behavior became same outlandish and extreme that many believe he was suffering from insanity. Some say he was driven to madness by the events in his life, while others say he may have been mentally ill or suffering the effects of a disease.
Caligula was the third Emperor of the Roman Empire
One of Caligula’s most egregious acts was in declaring that he was a living God. He ordered the construction of a bridge between his palace and the Temple of Jupiter, so that he could meet with the deity. He began appearing in public dressed as various gods and demigods such as Hercules, Mercury, Venus and Apollo. Reportedly, he began referring to himself as a god when meeting with politicians and he was referred to as Jupiter on occasion in public documents. Caligula had the heads removed from various statues of gods and replaced with his own in various temples.
As Caligula’s actions became more outrageous, the people of Rome began to hate him, and wished to rid him as their leader. At one point, Caligula declared to the Senate that he would be leaving Rome and moving to Egypt, where he would be worshipped as a living God. Cassius Chaerea of the Praetorian Guards began to plot towards Caligula’s demise. On January 24, 41 AD, a group of guards attacked Caligula after a sporting event. He was stabbed more than 30 times, and upon his death, he was buried in a shallow grave. Chaerea was said to have been the first to stab Caligula, with others joining in afterwards. His wife and daughter were also stabbed and killed. After his death, the Senate pushed to have him erased from Roman history, ordering destruction of his statues, and moving quickly to restore the Republic. The people of Rome were angry, and demanded revenge against those who murdered their Emperor. Caligula’s uncle, Claudius, became the next Emperor, and ordered the deaths of Chaerea and anyone who was involved in Caligula’s death.
Original: The Madness of Caligula