An isthmus is a narrow strip of land that connects two larger pieces of land, with water on both sides. Picture it like a natural bridge of earth between two bigger areas that would otherwise be separated by water.

A famous example is the Isthmus of Panama, which connects North America and South America. For millions of years, these continents were separated by ocean. Then, about three million years ago, volcanic activity and shifting plates formed this narrow land bridge. Animals could suddenly migrate between continents, and later, people could travel overland between them. Before the Panama Canal was built in 1914, ships had to sail all the way around South America to get from the Atlantic to the Pacific Ocean.

Other notable isthmuses include the Isthmus of Corinth in Greece, which connects the Peloponnese peninsula to mainland Greece, and the Isthmus of Suez in Egypt, which connects Africa to Asia.

Geographers and historians pay special attention to isthmuses because they often become important trade routes, military positions, or places where people eventually dig canals to save ships from taking much longer journeys.