Gaius Caesar Augustus Germanicus (31 August 12 24 January 41), better known by his nickname Caligula (), was the third Roman emperor, ruling from 37 to 41. The son of the popular Roman general Germanicus and Augustus' granddaughter Agrippina the Elder, Caligula was born into the first ruling family of the Roman Empire, conventionally known as the Julio-Claudian dynasty.

Germanicus' uncle and adoptive father, Tiberius, succeeded Augustus as emperor of Rome in AD 14. Although Gaius was named after Gaius Julius Caesar, he acquired the nickname "Caligula" ("little caliga," a type of military boot) from his father's soldiers during their campaign in Germania. When Germanicus died at Antioch in 19, Agrippina returned with her six children to Rome, where she became entangled in a bitter feud with Tiberius. The conflict eventually led to the destruction of her family, with Caligula as the sole male survivor. In 26, Tiberius withdrew from public life to the island of Capri, and in 31, Caligula joined him there. Following the death of Tiberius in 37, Caligula succeeded him as emperor.

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. While the reliability of these sources is questionable, it is known that during his brief reign, Caligula worked to increase the unconstrained personal power of the emperor, as opposed to countervailing powers within the principate. He directed much of his attention to ambitious construction projects and luxurious dwellings for himself, and he initiated the construction of two aqueducts in Rome: the Aqua Claudia and the Anio Novus. During his reign, the empire annexed the client kingdom of Mauretania as a province.

In early 41, Caligula was assassinated as a result of a conspiracy by officers of the Praetorian Guard, senators, and courtiers. However, the conspirators' attempt to use the opportunity to restore the Roman Republic was thwarted. On the day of the assassination of Caligula, the Praetorians declared Caligula's uncle, Claudius, as the next Roman emperor. Although the Julio-Claudian dynasty continued to rule the empire until the fall of his nephew Nero in 68, Caligula's death marked the official end of the Julii Caesares in the male line.

The Roman Senate (Latin: Senātus Rōmānus) was a governing and advisory assembly in ancient Rome. It was one of the most enduring institutions in Roman history, being established in the first days of the city of Rome (traditionally founded in 753 BC). It survived the overthrow of the Roman monarchy in 509 BC; the fall of the Roman Republic in the 1st century BC; the division of the Roman Empire in AD 395; and the fall of the Western Roman Empire in 476; Justinian's attempted reconquest of the west in the 6th century, and lasted well into the Eastern Roman Empire's history.

During the days of the Roman Kingdom, most of the time the Senate was little more than an advisory council to the king, but it also elected new Roman kings. The last king of Rome, Lucius Tarquinius Superbus, was overthrown following a coup d'état led by Lucius Junius Brutus, who founded the Roman Republic.

During the early Republic, the Senate was politically weak, while the various executive magistrates were quite powerful. Since the transition from monarchy to constitutional rule was most likely gradual, it took several generations before the Senate was able to assert itself over the executive magistrates. By the middle Republic, the Senate had reached the apex of its republican power. The late Republic saw a decline in the Senate's power, which began following the reforms of the tribunes Tiberius and Gaius Gracchus.

After the transition of the Republic into the Principate, the Senate lost much of its political power as well as its prestige. Following the constitutional reforms of Emperor Diocletian, the Senate became politically irrelevant. When the seat of government was transferred out of Rome, the Senate was reduced to a purely municipal body. That decline in status was reinforced when Constantine the Great created an additional senate in Constantinople.

After Romulus Augustulus was deposed in 476, the Senate in the West Empire functioned under the rule of Odoacer (476–489) and during Ostrogothic rule (489–535). It was restored to its official status after the reconquest of Italy by Justinian I but ultimately disappeared after 603, the date of its last recorded public act. Some Roman aristocrats in the Middle Ages bore the title senator, but it was by this point a purely honorific title and does not reflect the continued existence of the classical Senate. The Eastern Senate survived in Constantinople through the 14th century.