Thasos or Thassos is an island in the northern Aegean Sea, close to the coast of Thrace and the plain of the river Nestos (during the Ottoman times Kara-Su).

The island was colonized at an early date by Phoenicians, attracted probably by its gold mines; they founded a temple to the god Melqart, whom the Greeks identified as "Tyrian Heracles", and whose cult was merged with Heracles in the course of the island's Hellenization;[1] the temple still existed in the time of Herodotus.[2] An eponymous Thasos, son of Phoenix— or of Agenor, as Pausanias reported— is said to have been the leader of the Phoenicians, and to have given his name to the island.

In 720 708 BC, Thasos received a Greek colony from Paros. It was in a war which the Parian colonists waged with the Saians, a Thracian tribe, that the poet Archilochus threw away his shield. The Greeks extended their power to the mainland, where they owned gold mines which were even more valuable than those on the island. From these sources the Thasians drew great wealth, their annual revenues amounting to 200 or even 300 talents. Herodotus, who visited Thasos, says that the best mines on the island were those which had been opened by the Phoenicians on the east side of the island facing Samothrace.

The place was important during the Ionian Revolt against Persia. After the capture of Miletus (494 BC) Histiaeus, the Ionian leader, laid siege to Thasos. The attack failed, but, warned by the danger, the Thasians employed their revenues to build war ships and strengthen their fortifications. This excited the suspicions of the Persians, and Darius compelled them to surrender their ships and pull down their walls. After the defeat of Xerxes the Thasians joined the Delian confederacy; but afterwards, on account of a difference about the mines and marts on the mainland, they revolted.

The Athenians defeated them by sea, and, after a siege that lasted more than two years, took the capital, Thasos, probably in 463 BC, and compelled the Thasians to destroy their walls, surrender their ships, pay an indemnity and an annual contribution (in 449 BC this was 21 talents, from 445 BC about 30 talents), and resign their possessions on the mainland. In 411 BC, at the time of the oligarchical revolution at Athens, Thasos again revolted from Athens and received a Lacedaemonian governor; but in 407 BC the partisans of Lacedaemon were expelled, and the Athenians under Thrasybulus were admitted.

After the Battle of Aegospotami (405 BC), Thasos again fell into the hands of the Lacedaemonians under Lysander who formed a decarchy there; but the Athenians must have recovered it, for it formed one of the subjects of dispute between them and Philip II of Macedonia. In the embroilment between Philip III of Macedonia and the Romans, Thasos submitted to Philip, but received its freedom at the hands of the Romans after the battle of Cynoscephalae (197 BC), and it was still a "free" state in the time of Pliny.

Thasos was part of the Eastern Roman Empire, later known as Byzantine Empire. It was captured by the Turks in 1462. A brief revolt against Ottoman rule in 1821, led by Hajiyorgis Metaxas, failed. The island was given by the Sultan Mahmud II to Mehemet Ali of Egypt as a personal fiefdom in the late 1820s, as a reward for Egyptian intervention in the War of Greek Independence (which failed to prevent the creation of the modern Greek state). Egyptian rule was relatively benign (by some accounts Mehemet Ali had either been born or spent his infancy on Thasos) and the island became prosperous, until 1908, when the New Turk regime asserted Turkish control. On October 20, 1912 during the First Balkan War, a Greek naval detachment claimed Thasos as part of Greece, which it has remained since. During Axis occupation (1941-1944) Thasos, along with the rest of Eastern Macedonia and Tharace, was under Bulgarian control and suffered from hunger and forced recruitment of young men as slave laborers. The Bulgarians planned to annex the territory uder their control and closed down schools as a first step towards forced Bulgarization. Mountainous terrain facilitated small-scale resistance activity. The Greek Civil War affected the island in the form of skirmishes and Communist guerilla attacks until 1950, almost a year after the main histilities were over on the mainland.

Thasos, the capital, stood on the north side of the island, and had two harbours. Archilochus described Thasos as "an ass's backbone crowned with wild wood," and the description still suits the mountainous island with its forests of fir. The highest mountain, Ipsario or Ypsario, is 1045 m (3428 ft) high. Besides its gold mines, the wine, nuts and marble of Thasos were well known in antiquity. Thasian wine (a light bodied wine with a characteristic apple scent) was, in particular, quite famous; to the point where all Thasian coins carried the head of the wine god on one side and bunches of grape of the other.

Today, Thasos (informally known as Limenas, or "the port") is a part of the Kavala prefecture and is the southernmost and the easternmost points in the prefecture. Under local government reform in the late 1990s, the entire island became a single municipality. Thasos is served ferry routes to and from Kavala and Keramoti. The latter is a port at the eastern portion of the prefecture, close to Kavala's airport, and has the shortest possible crossing to the island.

The highest elevation of Thasos is the Ypsario, at 1,204 m. The main agricultural production on the island are honey and olive oil as well as wine, sheep, goat herding and fishing. Other industries includes lumber and tourism. Mining industry including lead, zinc and marble especially in the Panagia area where one of the mountains near the Thracian Sea has a large marble quarry. A marble quarry in the south has been mined during the ancient times. By far the most important economic activity is tourism.