Year 330 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Consulship of Crassus and Venno (or, less frequently, year 424 Ab urbe condita). The denomination 330 BC for this year has been used since the early medieval period, when the Anno Dominicalendar era became the prevalent method in Europe for naming years.
January 20 – Alexander the Great defeats the Persians, led by satrap Ariobarzanes, at the Persian Gates. In this battle, Ariobarzan, supported by only 700 Persian Immortals, holds the vast Macedonian army of 17,000 men at bay for 30 days. At the end, his troops are surrounded by Alexander's army, because of a Persian shepherd, who leads it around the Persian defenses. However, instead of surrendering, Ariobarzan and his 700 Immortals fight to the last man. Some historians consider him to be the Leonidas of Persia.
January 30 – After gaining the Pass of the Persian Gates, Alexander enters Persepolis. There he ceremonially burns down the palace of Xerxes I, as a symbol that the Panhellenic war of revenge is at an end.
Before continuing his pursuit of Darius III, who has retreated into Bactria, Alexander assembles all the Persian treasure and entrusts it to Harpalus, who is to hold it at Ecbatana as chief treasurer. Parmenion is also left behind in Media to manage communications between Alexander and the rest of his rapidly growing lands.
Crossing the Elburz Mountains to the Caspian Sea, Alexander seizes Zadracarta in Hyrcania and receives the submission of a group of satraps and Persian notables, some of whom he confirms in their offices. He then travels westward and defeats the Mardi, a mountain people who inhabit the Elburz Mountains. He also accepts the surrender of Darius' Greek mercenaries.
At Phrada, in Drangiana, Philotas, Parmenion's son and commander of the elite Macedonian companion cavalry, is implicated in an alleged plot against Alexander's life. He is condemned by the army, and executed. A secret message is sent by Alexander to Cleander, Parmenion's second in command, who obediently kills Parmenion at Ecbatana in Media for fear that he would rise up in revolt at the news of his son's death. All Parmenio's adherents are now eliminated and men close to Alexander are promoted.
Alexander's regent in Macedonia, Antipater, makes peace with the Thracians (with whom he has been warring) and then marches south with a large force of over 40,000 men. He wins a hard-fought Battle of Megalopolis in Arcadia against Agis III of Sparta and his Greek mercenaries. Agis III is killed, and Spartan resistance is broken.
Aeschines continues to try to prevent Demosthenes from being awarded a golden crown for his services to Athens. The case, which has begun in 336 BC, finally concludes with the overwhelming defeat of Aeschines, largely because of Demosthenes' brilliant speech for Ctesiphon (On the Crown).
Following his defeat in the courts by Demosthenes, Aeschines leaves Athens for Rhodes, to teach rhetoric.