Phocaea or Phokaia (Ancient Greek: Φώκαια, Phókaia; modern-day Foça in Turkey) was an ancient Ionian Greek city on the western coast of Anatolia. Greek colonists from Phocaea founded the colony of Massalia (modern-day Marseille, in France) in 600 BC, Emporion (modern-day Empúries, in Catalonia, Spain) in 575 BC and Elea (modern-day Velia, in Campania, Italy) in 540 BC.

Phocaea was the northernmost of the Ionian cities, on the boundary with Aeolis. It was located near the mouth of the river Hermus (now Gediz), and situated on the coast of the peninsula separating the Gulf of Cyme to the north, named for the largest of the Aeolian cities, and the Gulf of Smyrna (now İzmir) to the south.

Phocaea had two natural harbours within close range of the settlement, both containing a number of small islands. Phocaea's harbours allowed it to develop a thriving seafaring economy, and to become a great naval power, which greatly influenced its culture.^{[citation needed]}

Recent archaeological surveys have shown that the city of Phocaea was large for the archaic period. Herodotus gives an idea of the size of Phocaea by describing the walls of Phocaea as having a length of several stadia.

A 4th century BC Persian tomb, known as Tas Kule (rock tower), stands (38°39′37″N 26°49′2″E / 38.66028°N 26.81722°E / 38.66028; 26.81722) 7 km (4.3 mi) east of Phocaea along a main road. This funerary monument was carved out of solid rock with a lower 2.7 meters (8 ft 10 in) high rectangular story (9 by 6 meters (30 ft × 20 ft)) surmounted by a second 1.9 meters (6 ft 3 in) high story (3 by 3 meters (9.8 ft × 9.8 ft)). Four steps between the two levels suggest strong Persian influence and most archaeologists believe this tomb was built for a Persian aristocrat or local leader serving the Persians. Compare the style of the tomb of Cyrus.

The ancient Greek geographer Pausanias says that Phocaea was founded by Phocians under Athenian leadership, on land given to them by the Aeolian Cymaeans, and that they were admitted into the Ionian League after accepting as kings the line of Codrus. Pottery remains indicate Aeolian presence as late as the 9th century BC, and Ionian presence as early as the end of the 9th century BC. From this an approximate date of settlement for Phocaea can be inferred.

According to Herodotus the Phocaeans were the first Greeks to make long sea-voyages, having discovered the coasts of the Adriatic, Tyrrhenia and Spain. Herodotus relates that they so impressed Arganthonios, king of Tartessus in Spain, that he invited them to settle there, and, when they declined, gave them a great sum of money to build a wall around their city.

Their sea travel was extensive. To the south they probably conducted trade with the Greek colony of Naucratis in Egypt, which was the colony of their fellow Ionian city Miletus. To the north, they probably helped settle Amisos (Samsun) on the Black Sea, and Lampsacus at the north end of the Hellespont (now the Dardanelles). However, Phocaea's major colonies were to the west. These included Alalia in Corsica, Emporiae and Rhoda in Spain, and especially Massalia (Marseille) in France.