Isthmuses are narrow strips of land bordered on two sides by large expanses of water. Fictional isthmuses are often sites of roads or paths connecting two areas. These routes may be dangerous, full of cliffside pathways and the potential ambush. There may be sea caves within the isthmus that allow ships to cross from one body of water to the other. As tides rise and fall, sea gaps may open in the isthmus, also allowing for sea traffic or tidal flats may form, allowing for foot traffic. As isthmuses naturally create a funnel for ground movement towns, cities, and other settlements may have been established on them or nearby. Trade routes may need to cross their span.