Aristagoras (Greek: Ἀρισταγόρας ὁ Μιλήσιος) was the leader of Miletus in the late 6th century BC and early 5th century BC and a key player during the early years of the Ionian Revolt against the Persian Achaemenid Empire.
Aristagoras served as deputy governor of Miletus, a polis on the western coast of Anatolia around 500 BC. He was the son of Molpagoras, and son-in-law (and nephew) of Histiaeus, whom the Persians had set up as tyrant of Miletus. Aristagoras controlled Miletus while Histiaeus was being held by the Achaemenid King Darius I of Persia at Susa. Aristagoras was the main orchestrator of the Ionian Revolt, when the Greek poleis of Ionia on the east coast of the Aegean Sea banded together to rebel against rule by the Achaemenid Empire.
Certain exiled citizens of Naxos came to Miletus to seek refuge. They asked Aristagoras to supply them with troops, so that they could regain control of their homeland. Aristagoras considered that if he was able to supply troops to the Naxians, then he could become ruler of Naxos. So he agreed to assist the Naxians. He explained that he did not have enough troops of his own, but that Artaphernes, Darius’ brother and the Persian satrap of Lydia, who commanded a large army and navy on the coast of Asia, could help supply troops. The Naxians agreed to Aristagoras seeking Artaphernes' support and supplied him with money.
Aristagoras travelled to Sardis and told Artaphernes to attack Naxos and restore the exiles with the implication that Artaphernes would then gain control of the island. He explained to Artaphernes that Naxos “was a fine and fertile island, close to the Ionian coast, and rich both in treasures and slaves.” Aristagoras promised that he would both fund the expedition and give Artaphernes a bonus sum. He also tempted Artaphernes by adding that capturing the island would place other poleis of the Cyclades under his control, which would serve as a base for attacking Euboea. Artaphernes agreed and promised 200 ships. The following spring, Aristagoras and the Naxian exiles sailed with the fleet. Unfortunately for the success of the invasion, Aristagoras quarrelled with the Persian admiral Megabates, who then informed the Naxians that the fleet was coming. Naxos then had enough time to prepare for a siege. Four months later, the siege still held, the Persians were out of supplies and had only limited funds remaining. The expedition was then considered a failure and the Persians sailed home.