Andros (Άνδρος, ˈanðros) is the northernmost island of the Greek Cyclades archipelago, about southeast of Euboea, and about north of Tinos. It is nearly long, and its greatest breadth is . It is for the most part mountainous, with many fruitful and well-watered valleys. The municipality, which includes the island Andros and several small, uninhabited islands, has an area of . The largest towns are Andros (town), Gavrio, Batsi, and Ormos Korthiou.
Palaeopolis, the ancient capital, was built into a steep hillside, and the breakwater of its harbor can still be seen underwater. At the village of Apoikia, there is the notable spring of Sariza, where the water flows from a sculpted stone lion's head. Andros also offers hiking options with many new paths being added each year.
During the Final Neolithic (over 5,000 years ago), Andros had a fortified village on its west coast, which archaeologists have named Strofilias, after the plateau on which it was built. Strofilias was related to the "Attica-Kephala" culture, and predates the Cycladic culture of the Bronze Age. It was an important maritime centre and one of the earliest examples of fortification in Greece. It is notable for rock carvings on its walls, which include animals such as jackals, goats, deer, fish and dolphins, as well as a depiction of a flotilla of ships.
The island in ancient times contained an Ionian population, perhaps with an admixture of Thracian ancestry. Though it has been proposed that Andros was originally dependent on Eretria, by the 7th century BC it had become sufficiently prosperous to send out several colonies, to Chalcidice (Acanthus, Stageira, Argilus, Sane). The ruins of Palaeopolis, the ancient capital, are on the west coast; the town possessed a famous temple, dedicated to Dionysus. In 480 BC, it supplied ships to Xerxes and was subsequently harried by the Greek fleet. Though enrolled in the Delian League, it remained disaffected towards Athens, and in 477 had to be coerced by the establishment of a cleruchy on the island; nevertheless, in 411 Andros proclaimed its freedom, and in 408 withstood an Athenian attack.