Marmara is a Turkish island in the Sea of Marmara. It is the largest island in the Sea of Marmara that 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.
Its name derives from the Greek μάρμαρον (marmaron) and that from μάρμαρος (marmaros), "crystalline rock", "shining stone", perhaps from the verb μαρμαίρω (marmairō), "to flash, sparkle, gleam", because it is famous for its white marble.
In ancient times, the island was called Proconnesus. In 493 BC it was burned by a Phœnician fleet fighting for Darius. In 410 Alcibiades conquered it for Athens.
Under the name Proconnesus it is a titular see of the Roman Catholic Church. The see is currently vacant.
