The 40s ran from January 1, AD 40, to December 31, AD 49. Following the assassination of Caligula, Claudius became Roman emperor in AD 41. In AD 43 he sent Aulus Plautius with four legions across the Channel, initiating the decades-long Roman conquest of Britain.
The Trưng sisters' rebellion broke out in the far south of Han China in AD 40, when Vietnamese leader Trưng Trắc and her sister Trưng Nhị rose against Han authority in Jiaozhi, in what is now northern Vietnam. Han China dispatched General Ma Yuan to suppress the rebellion in AD 42. The Han army had suppressed the uprising by AD 43.
Christianity reached Egypt with the founding of the Church of Alexandria, whose first patriarch was Mark the Evangelist. James the Great, one of the Twelve Apostles and according to the New Testament, the first of them to be martyred, was killed in AD 44. Claudius expelled Jews from Rome at some point between AD 41 and 53. Scholars explain the measure to his concern with public order in Rome rather than a policy directed against Judaism.
A famine struck Judea between AD 44 and 48. Josephus records that Helena of Adiabene provided grain and dried figs to the people of Jerusalem, while her son Izates sent money to the city's leaders.
Literary works of this decade include the Histories of Alexander the Great, written by Quintus Curtius Rufus, and essays by Seneca (including De Ira; Ad Marciam, De Consolatione; De Brevitate Vitae; De Consolatione ad Polybium; and Ad Helviam Matrem, De Consolatione).
In the absence of reliable demographic data, estimates of the world population in the 1st century vary widely: figures for AD 1 ranging from 150 to 300 million. Demographers rarely attempt to estimate the population for most specific years in antiquity, instead giving approximate numbers for round years such as AD 1 or AD 200. Scott Manning has tentatively put the population in AD 40 at 247 million.
Philo teaches that all men are born free.
Emperor Caligula is consul without colleague.
Caligula starts on a campaign to conquer Britain, which fails miserably. He declares himself victorious regardless.
Noricum and Mauretania are incorporated into the Roman Empire.
Caligula reforms the principatus into a Hellenistic Autocracy. He distributes honors carelessly, declares himself a god and orders that all the heads of the Greek deity statues be replaced by his. He also appoints his horse, Incitatus, to the Senate.
Construction begins on the Pont du Gard aqueduct in Gallia Narbonensis (approximate date).
Christianity comes to Egypt as a church is founded in Alexandria. Mark the Evangelist founds the Church of Alexandria as the first Patriarch (traditional date).
An early Christian church is erected at Corinth (most probable date).
The traditional date of Saint James the Great meeting Our Lady of the Pillar in Spain.
The Germanic Quadi tribe begins settling in present-day Moravia and Slovakia.
Vardanes I becomes king of Parthia, opposed by his brother Gotarzes II.
The Vietnamese Trưng Sisters rebel against the rule of the Chinese Emperor Guang Wu of Han.