(interior valley), a closed depression typical of karst regions. Poljes have steep, and often perpendicular, walls and a more or less flat floor. Along the floor flow rivers, streams, or periodic currents, which disappear into ponors (sinkholes). Some poljes contain lakes or are periodically flooded by water. They range from 1 to 400 sq km in area. The classical form of polje is found on the Balkan Peninsula.