Year 40 (XL) in the Anno Domini (AD) system corresponds to the year commonly written as AD 40. In the Julian calendar it was a leap year that, by modern reconstructions, began on a Friday. The year is sometimes given in Roman sources by consular names rather than a numeric label.
Calendar and naming
The year is denoted XL in Roman numerals and, according to traditional reckoning, was a leap year of the Julian calendar. Contemporary Romans often identified years by the names of that year's consuls (a practice called consular dating); later medieval scholars and clerics adopted the Anno Domini system to count years from the traditionally estimated birth of Christ. Historical summaries sometimes note that AD 40 "started on Friday" in the Julian scheme: a weekday assignment that depends on correlation methods between ancient and modern calendars (Friday).
Political and social context
The Roman Empire in AD 40 was ruled by Emperor Caligula (reigned 37–41). His short decade of rule is remembered for increasing tensions between the imperial court and the Senate, as well as active involvement in provincial appointments and military matters. Beyond Rome, large imperial structures continued to shape life across the Mediterranean, and neighboring powers such as the Parthian realm maintained long-standing diplomatic and frontier relationships.
Regional developments
In the eastern half of Eurasia, the Eastern Han dynasty governed large areas of China under Emperor Guangwu, consolidating administrative reforms begun earlier in the first century. In the eastern Mediterranean and Judea, local client kings and Roman procurators administered affairs under imperial oversight. Meanwhile, early Christian groups and other new religious movements were spreading in small communities across cities of the Roman world.
Historical significance and usage
For modern historians the year functions as a chronological anchor within the early first century, useful for organizing events, inscriptions, and literary works. References to AD 40 appear in historical narratives, epigraphy, and chronological tables; scholars convert ancient consular or regnal dating into AD years to create continuous timelines.
- Often cited as a consular year in Roman records.
- Identified as part of the early Roman imperial period, during Caligula's reign.
- Chronological label useful when distinguishing AD 40 from 40 BC or the number 40 itself.
Because surviving evidence from any single year in antiquity is fragmentary, accounts of AD 40 are reconstructed from a mix of literary sources, inscriptions, coins and later historiography. For further chronology and calendrical details see standard references and conversion tables that relate Roman consular dating and the Julian calendar to the Anno Domini era.