|Centuries:||1st century BC – 1st century – 2nd century|
|Decades:||10s 20s 30s – 40s – 50s 60s 70s|
|Years:||37 38 39 – 40 – 41 42 43|
|Gregorian calendar||AD 40|
|Ab urbe condita||793|
|Balinese saka calendar||N/A|
|Chinese calendar||己亥年 (Earth Pig)|
2736 or 2676
— to —
庚子年 (Metal Rat)
2737 or 2677
|Coptic calendar||−244 – −243|
|- Vikram Samvat||96–97|
|- Shaka Samvat||N/A|
|- Kali Yuga||3140–3141|
|Iranian calendar||582 BP – 581 BP|
|Islamic calendar||600 BH – 599 BH|
|Julian calendar||AD 40|
|Minguo calendar||1872 before ROC|
|Seleucid era||351/352 AG|
|Thai solar calendar||582–583|
166 or −215 or −987
— to —
167 or −214 or −986
- The emperor Caligula is consul without colleague.
- Caligula starts a campaign to conquer Britain. It fails miserably. He names himself the winner.
- Noricum and Mauretania are added 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. According to legend, this is when he appointed his horse, Incitatus, a senator.
- Approximate date of start of construction on the Pont du Gard aqueduct in Gallia Narbonensis.
- Philo teaches that all men are born free.
- An early Christian church is erected at Corinth (most probable date).
- Vardanes I becomes king of Parthia. He was opposed by his brother Gotarzes II.
- The Vietnamese Trung sisters rebel against the rule of the Chinese Emperor Guangwu of Han.
- July 13 – Gnaeus Julius Agricola, Roman governor of Britain (d. 93 AD)
- Pedanius Dioscorides, Greek physician (approximate date) (d. 90 AD)
- Frontinus, Roman general and military author (approximate date) (d. 103)
- Dio Chrysostom, Greek philosopher and historian (approximate date d. c. 120)
- Claudia Octavia, daughter of Claudius and Messalina (d. 62)
- Empress Ma of the Han Dynasty (d. 79)