A strait is a narrow body of water that connects two larger bodies of water. It may be formed by a fracture in an isthmus, a narrow body of land that connects two bodies of water. Tectonic shifts can lead to straits like this. One strait that was formed by tectonic activity is the Strait of Gibraltar, the only link between the Mediterranean Sea and the Atlantic Ocean. If fractures in an isthmus are created by human activity, the straits are usually called canals. The Suez Canal was constructed in 1869 as a waterway between the Mediterranean Sea and the Red Sea. A strait can also be formed by a body of water overflowing land that has subsided or has been eroded. The Bosporus, which links the Black Sea and the Aegean Sea, was formed this way.