Year 321 BC was a year of the pre-Julian Roman calendar.
|Millennium:||1st millennium BC|
|Centuries:||5th century BC – 4th century BC – 3rd century BC|
|Decades:||350s BC 340s BC 330s BC – 320s BC – 310s BC 300s BC 290s BC|
|Years:||324 BC 323 BC 322 BC – 321 BC – 320 BC 319 BC 318 BC|
|321 BC by topic|
|State leaders – Sovereign states|
|Birth and death categories|
|Births – Deaths|
|Establishments and disestablishments categories|
|Establishments – Disestablishments|
|Gregorian calendar||321 BC|
|Ab urbe condita||433|
|Ancient Egypt era||XXXIII dynasty, 3|
|- Pharaoh||Ptolemy I Soter, 3|
|Ancient Greek era||114th Olympiad, year 4|
|Balinese saka calendar||N/A|
|Chinese calendar||己亥年 (Earth Pig)|
2376 or 2316
— to —
庚子年 (Metal Rat)
2377 or 2317
|Coptic calendar||−604 – −603|
|Ethiopian calendar||−328 – −327|
|- Vikram Samvat||−264 – −263|
|- Shaka Samvat||N/A|
|- Kali Yuga||2780–2781|
|Iranian calendar||942 BP – 941 BP|
|Islamic calendar||971 BH – 970 BH|
|Minguo calendar||2232 before ROC|
|Thai solar calendar||222–223|
−194 or −575 or −1347
— to —
−193 or −574 or −1346
|Wikimedia Commons has media related to 321 BC.|
- Antipater makes Antigonus commander in chief of his army in Asia Minor. He sends him with Craterus to fight against Eumenes, the satrap of Cappadocia and a supporter of Perdiccas.
- Perdiccas marches against Ptolemy. When he fails to cross the Nile he is murdered by mutinous officers. Ptolemy is in power in Egypt and Seleucus in power in Babylon.
- The main generals of the late Alexander the Great agree to the Partition of Triparadisus.
- Ptolemy strengthens his position by marrying Eurydice, the third daughter of Antipater.
- Antigonus and Craterus defeat Eumenes in battle. Eumenes escapes.
- Successes by Rome's armies force the Samnites to ask for peace. The terms are harsh so peace does not happen.
- Two Roman consuls, Spurius Postumius Albinus and Titus Veturius Calvinus, leading a force into Samnium. They are trapped in a mountain pass known as the Caudine Forks. They make a five-year treaty with the Samnites.