Chios is a city of 25,000 inhabitants. It is the main seaport and industrial center of the island, built on the old city of Chios, remnants of which include the old theatre and the city walls. A mediaeval castle is also found in the city, of Byzantine origin, which was expanded later by the Genoese and the Ottomans.
Modern structures include the Korai Library, the Byzantine Museum and the Ethnological Museum. The main square of the city centre of Chios is called Vounakio Square. It is the starting point of most bus lines to various towns in the island.