The island has been inhabited since at least the Neolithic era, with an early Cycladic fortified settlement and burial ground at Kastri in the island’s northeast dating from 2800 to 2300 BC.
The Venetians seized control of the island from the Byzantines in 1204 and remained until 1522, during which time most of the Greek islanders adopted Catholicism. Even during the centuries of Ottoman rule which followed, the island maintained a largely Catholic identity.
During the War of Independence, thousands of Orthodox refugees from islands ravaged by the Turks fled to Syros. They brought an infusion of Greek Orthodoxy and a fresh entrepreneurial drive that made Syros the commercial, naval and cultural centre of Greece during the 19th century. Syros’ position declined in the 20th century, but you still see shipyards, textile manufacturing, thriving horticulture, a sizeable administrative sector, a university campus and a continuing Catholic population.