The Black Sea is a large inland sea situated between Southeastern Europe and Western Asia. It is connected to the Mediterranean via the Bosphorus Strait, the Sea of Marmara, and the Dardanelles. A fascinating geographical feature of the Black Sea is that it is the world's largest meromictic basin. This means that its upper layers of water do not mix with the deeper, more saline layers. As a result, below a depth of about 150-200 meters, the water is 'anoxic'—entirely devoid of oxygen. Because there is no oxygen to support wood-boring organisms or decay, ancient shipwrecks from thousands of years ago have been found at the bottom in a state of nearly perfect preservation. Historically, the Black Sea has been a strategic hub for trade and naval power, bordered by Turkey, Bulgaria, Romania, Ukraine, Russia, and Georgia. It is also the destination for major European rivers like the Danube and the Dnieper.