Following the Revolution of 1821, traditional marine centres such as Hydra, Spetses and Galaxidi lost the leading position they had previously held in the Greek area. On the other hand Syros, which in the 1830s had limited itself to fishing, farming and stockbreeding on a scale that on the whole did not go beyond local needs, gradually turned into a transit trade and marine centre. The limited control exercised by the sultan and the special privileges enjoyed by the island's residents, Catholic in their majority and thus under the protection of France, in conjunction with the neutral stance they had maintained during the Struggle for Independence, made Syros a safe haven for refugees fleeing from the islands of the Archipelago and Asia Minor. They came for the most part from Chios, Aivali, Smyrna, Psara, Kassos, Crete and to a lesser extent from mainland Greece. Soon commercial companies, in which Chiots played the leading part, were established. Shipyards were built and here it was the Psarians who led the way. The town of the refugees was built around the port of the island and was named Hermoupolis, after Hermes, the God of Merchants.

The people of Hermoupolis, using their own funds, loans from the Greeks of the diaspora and above all the commercial know-how they had acquired in the lands they had come from, made Syros a centre of exchange between East and West. Loads of grain from the Eastern Mediterranean and industrial products from the West passed through the island's port. It is worth noting that between 1851 and 1858 the revenues of the Syros customs were above 70% of the total revenues of the Greek state. Along with the island's shipyards merchant shipping was organized. The sailing ships of Syros had a large share in the transport of products traded by the island's merchants. Significant also was the presence of tanneries at a time when secondary production was still practically non-existent.

The island's decline started in the second half of the 19th century. The development of steam shipping played a significant part in this process. Steamships permitted direct connection between East and the West and thus Syros became redundant as a transit trade port. In the same period the opening of the Corinth Canal made Piraeus the major port and commercial centre of Greece.