The Sea of Marmara, Turkey

The Sea of Marmara (also known as the Marmara Sea) is an inland sea located entirely within Turkey. It serves as a natural bridge between the Black Sea and the Aegean Sea, separating the country’s European region of Thrace from Anatolia in Asia. This strategically important waterway has played a vital role in trade, navigation, and history for thousands of years.

The sea is connected to the Black Sea by the Bosporus Strait and to the Aegean Sea through the Dardanelles Strait. The Bosporus also divides the city of Istanbul into its European and Asian sides, making the Sea of Marmara a key link between two continents.

Covering an area of approximately 11,350 square kilometres (4,382 square miles), the Sea of Marmara stretches about 280 kilometres from east to west and up to 80 kilometres across at its widest point. Its deepest section reaches approximately 1,370 metres (4,495 feet).

The sea has an average salinity of about 22 parts per thousand, making it slightly saltier than the Black Sea but considerably less saline than the open oceans. At greater depths, however, salinity increases to around 38 parts per thousand, similar to that of the Mediterranean Sea. Due to the higher density of this deep saline water, it remains beneath the surface and mixes only minimally with the upper layers.

Several rivers, including the Biga, Gönen, Susurluk, and Kocabaş (ancient Granicus) rivers, flow into the Sea of Marmara, contributing freshwater that helps reduce surface salinity. Most of these rivers originate in Anatolia, as relatively little land in the Thrace region drains southward into the sea.

Two notable island groups lie within the Sea of Marmara: the Princes’ Islands, located near Istanbul, and the Marmara Islands in the southwestern part of the sea. The Marmara Islands have been famous since antiquity for their rich marble quarries. In fact, the sea derives its name from the Greek word mármaron, meaning “marble.”

Beneath the Sea of Marmara runs the North Anatolian Fault, one of the world’s most active seismic fault systems. This fault has been responsible for numerous devastating earthquakes, including the 1999 İzmit Earthquake, making the region one of Turkey’s most significant seismic zones.

In ancient times, the sea was known as Propontis, a Greek name meaning “the sea before the sea” (pro meaning “before” and pontos meaning “sea”). For ancient Greek sailors travelling from the Aegean toward the Black Sea, the Sea of Marmara was the body of water encountered before entering the Black Sea.

According to Greek mythology, the Argonauts encountered a violent storm while crossing the Propontis, forcing them back to the island of Cyzicus. Mistaking the returning heroes for enemies, King Cyzicus and his warriors attacked them during the night. In the ensuing battle, the king was accidentally killed by either Jason or Heracles, depending on the version of the legend. The tragic story remains one of the most famous myths associated with the Sea of Marmara.

Today, the Sea of Marmara is not only a crucial maritime route connecting the Mediterranean and Black Seas but also an important destination for tourism, sailing, fishing, and coastal recreation. Its scenic islands, historic ports, and unique position between Europe and Asia make it one of Turkey’s most fascinating and strategically significant bodies of water.