The Sea of Marmara (Turkish: Marmara Denizi, Modern Greek: Θάλασσα του Μαρμαρά or Προποντίδα) (also known as the Sea of Marmora or the Marmara Sea) is an inland sea that connects the Black Sea to the Aegean Sea, thus separating Asia Minor from Europe. The Bosporus connects it to the Black Sea and the Dardanelles to the Aegean. The former also separates Istanbul into its Asian side and European side. It has area of 11,350 square kilometres.
There are two major island groups known as the Prince's and Marmara islands. The latter group is rich in sources of marble and gives the sea its name (Greek marmaros, marble).
The North Anatolian fault, which has triggered many major earthquakes in recent years, such as the Izmit Earthquake of 1999, runs under the sea.
Propontis (Προποντίς, -ίδος < pro 'before' + pontos 'Black Sea') was the ancient Greek name for the sea.