|Centuries:||1st century BC – 1st century – 2nd century|
|Decades:||20s BC 10s BC 0s BC – 0s – 10s 20s 30s|
|Years:||1 BC 1 AD 2 AD – 3 AD – 4 AD 5 AD 6 AD|
|3 by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishment and disestablishment categories|
|Establishments – Disestablishments|
|Ab urbe condita||756|
|Bahá'í calendar||−1841 – −1840|
|English Regnal year||N/A|
|Chinese calendar||壬戌年 (Water Dog)
2699 or 2639
— to —
癸亥年 (Water Pig)
2700 or 2640
|Coptic calendar||−281 – −280|
|Ethiopian calendar||−5 – −4|
|- Vikram Samvat||59–60|
|- Shaka Samvat||N/A|
|- Kali Yuga||3104–3105|
|Igbo calendar||−997 – −996|
|Iranian calendar||619 BP – 618 BP|
|Islamic calendar||638 BH – 637 BH|
|Minguo calendar||1909 before ROC
|Thai solar calendar||546|
|Wikimedia Commons has media related to 3.|
Year 3 (III) was a common year starting on Tuesday (link will display the full calendar) of the Julian calendar (the sources differ, see leap year error for further information) and a common year starting on Monday of the Proleptic Julian calendar. At the time, it was known as the Year of the Consulship of Lamia and Servilius (or, less frequently, year 756 Ab urbe condita). The denomination 3 for this year has been used since the early medieval period, when the Anno Domini calendar era became the prevalent method in Europe for naming years.
- The rule of emperor Augustus is renewed for a ten-year period.
- Augustus adopts his grandson, Gaius Caesar, with the expectation that he will succeed him. Gaius is made proconsul and is sent on a special mission to the East.
- Lucius Aelius Lamia and Marcus Valerius Messalla Messallinus are consuls of Rome.
- Menneas becomes Archon of Athens.
- Five German tribes are unified by Marbod, King of the Marcomanni. The unification of the five tribes represents a direct threat to Rome in the area that will become Silesia and Saxony.
- King Yuri of Goguryeo moved the capital from Jolbon Fortress to Gungnae Fortress.
- Wang Mang foils a plot by his son, Wang Yu, his brother-in-law, Lu Kuan, and the Wei clan to oust him from the regent's position. Wang Yu and Lu Kuan are killed in the purge that follows.