|Millennium:||1st millennium BC|
|209 BC by topic|
|Gregorian calendar||209 BC|
|Ab urbe condita||545|
|Ancient Egypt era||XXXIII dynasty, 115|
|- Pharaoh||Ptolemy IV Philopator, 13|
|Ancient Greek era||142nd Olympiad, year 4|
|Balinese saka calendar||N/A|
|Chinese calendar||辛卯年 (Metal Rabbit)|
2488 or 2428
— to —
壬辰年 (Water Dragon)
2489 or 2429
|Coptic calendar||−492 – −491|
|Ethiopian calendar||−216 – −215|
|- Vikram Samvat||−152 – −151|
|- Shaka Samvat||N/A|
|- Kali Yuga||2892–2893|
|Iranian calendar||830 BP – 829 BP|
|Islamic calendar||856 BH – 854 BH|
|Minguo calendar||2120 before ROC|
|Seleucid era||103/104 AG|
|Thai solar calendar||334–335|
−82 or −463 or −1235
— to —
−81 or −462 or −1234
Year 209 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Verrucosus and Flaccus (or, less frequently, year 545 Ab urbe condita). The denomination 209 BC 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 Romans under Quintus Fabius Maximus Verrucosus capture Tarentum (modern Taranto), which the Carthaginian general Hannibal has held for three years.
- The Battle of Canusium is fought between Hannibal's Carthaginian army and a Roman force led by Marcus Claudius Marcellus. The battle is indecisive.
- From his headquarters at Tarraco (Tarragona), Publius Cornelius Scipio, the Roman commander in Spain, launches a combined military and naval assault on the Carthaginian headquarters at Carthago Nova (modern-day Cartagena). He successfully besieges and captures the city. In capturing this city, Scipio gains access to copious stores and supplies, Spanish hostages, the local silver mines, a splendid harbour and a base for an advance farther south.
- The King of the Parthians, Arsaces II, is attacked by the Seleucid king Antiochus III, who takes Hecatompylos (southeast of the Caspian Sea), the Arsacid capital and Syrinx in Hyrcania. Antiochus III defeats Arsaces II at the Battle of Mount Labus and then forces Arsaces II to enter into an alliance with the Seleucids.
- As strategos of the Achaeans, the Greek general Philopoemen is responsible for turning the Achaean League into an aggressive military power. He builds up the League's military capability. The Achaean League's army and cavalry under Philopoemen then defeat the Aetolians on the Elean frontier.
- Modun khaan inherits Teoman's Hunnu confederations and founds the Xiongnu Empire. Modu's forces push into Northern China, threatening the Qin Empire and forcing them to further fortify the Great Wall.
First year of the reign of the Second Emperor of the Qin Dynasty.