Marmara Island (Turkish: Marmara Adası) is a Turkish island in the Sea of Marmara. With an area of 117.8 km2 (45.5 sq mi) it is the largest island in the Sea of Marmara and is the second largest island of Turkey after Gökçeada (older name in Turkish: İmroz; Greek: Ίμβρος Imvros). It is the center of Marmara district in Balıkesir Province. Transportation is possible from Istanbul by ship and ferry, and by motorboat from Tekirdağ and Erdek. Famed for their wine and fish, Marmara and Avsa offer wonderful shorelines. Marmara island is full of historical treasures which increase its attractiveness. The town of "Mermer Plaj" / Marble Beach takes its name from the marbles for which the town is famous and which give the island and the sea their name.
In ancient times the island was called Proikonesos (Προικόνησος) or Prokonnesos (Προκόννησος), Latinized as Proconnesus. The modern name "Marmara" is derived from the Greek μάρμαρον (marmaron) and that from μάρμαρος (mármaros), "crystalline rock", "shining stone", perhaps from the verb μαρμαίρω (marmaírō), "to flash, sparkle, gleam", because it was famous for the white marble quarried there. Under the name Proconnesus it is a titular see of the Roman Catholic Church (the see has been vacant since the death in 1963 of the most recent occupant), and of the Ecumenical Patriarchate of Constantinople.