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|Millennium:||1st millennium BC|
|390 BC by topic|
|Gregorian calendar||390 BC
|Ab urbe condita||364|
|Ancient Egypt era||XXIX dynasty, 9|
|- Pharaoh||Hakor, 4|
|Ancient Greek era||97th Olympiad, year 3|
|Balinese saka calendar||N/A|
|Chinese calendar||庚寅年 (Metal Tiger)
2307 or 2247
— to —
辛卯年 (Metal Rabbit)
2308 or 2248
|Coptic calendar||−673 – −672|
|Ethiopian calendar||−397 – −396|
|- Vikram Samvat||−333 – −332|
|- Shaka Samvat||N/A|
|- Kali Yuga||2711–2712|
|Iranian calendar||1011 BP – 1010 BP|
|Islamic calendar||1042 BH – 1041 BH|
|Minguo calendar||2301 before ROC
|Thai solar calendar||153–154|
−263 or −644 or −1416
— to —
−262 or −643 or −1415
|Wikimedia Commons has media related to 390 BC.|
Year 390 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Tribunate of Ambustus, Longus, Ambustus, Fidenas, Ambustus and Cornelius (or, less frequently, year 364 Ab urbe condita). The denomination 390 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.
- July 18 – Battle of the Allia: Brennus, a chieftain of the Senones of the Adriatic coast of Italy, leads an army of Cisalpine Gauls in their attack on Rome. They capture the entire city of Rome except for the Capitoline Hill, which is successfully held against them. However, seeing their city devastated, the Romans attempt to buy their salvation from Brennus. The Romans agree to pay one thousand pounds weight of gold.
- While Brennus is arguing over the weight of the gold with the Romans, the exiled dictator Marcus Furius Camillus appears with an army and refuses to allow him to take the gold. In an initial battle through Rome's streets, the Gauls are ejected from the city and in a second battle away from the city, Camillus defeats the invaders, earning the title of the "Second Founder of Rome" for saving the city.
- The Pharaoh of Egypt, Hakor (Akoris), concludes a tripartite alliance with Evagoras, king of Cyprus, and Athens.
- The Tollund Man (approximate date, based on his being forty years old at the time of death)