Excavations of an Early Cycladic fortified settlement and burial ground at Kastri in the island’s northeast date from the Neolithic period (2800–2300 BC).
During the medieval period Syros had an overwhelmingly Roman Catholic population. Capuchin monks and Jesuits settled on the island during the 17th and 18th centuries, and such was the Catholic influence that France was called upon by Syros to help it during Turkish rule. Later Turkish influence was benevolent and minimal and Syros busied itself with shipping and commerce. During the War of Independence thousands of refugees from islands ravaged by the Turks fled to Syros. They brought with them an infusion of Greek Orthodoxy and a fresh commercial drive that made Syros the commercial, naval and cultural centre of Greece during the 19th century. This position was lost to Piraeus in the 20th century. The island’s industrial mainstay of shipbuilding has declined, but Syros still has textile manufacturing, a thriving horticultural sector, a sizable administrative and service sector and a small but healthy tourism industry.