A berm is essentially a circular mound of dirt (and occasionally fill) constructed on an otherwise level stretch of ground to improve the design of a property. The rounded shape of a berm separates it from a raised bed. The latter has a rectangular form and a flat surface. Berms are commonly used in residential landscaping to divide up the yard, make planting easier, and provide better drainage. There are two main types of berms: natural and made-up. Natural berms are formed when soil is eroded away by water and leaves an uneven surface that can range from soft depressions filled with rainwater to hard cliffs overlooking dry valleys. These berms often contain plants such as gorse or hawthorn trees found in Welsh hedges. Made-up berms are created by humans and usually consist of layers of different materials including soil, sand, gravel, and stone. These behemoths can get very large; some have been known to cover acres of land. They are common in coastal and riverine environments where their use helps reduce erosion and creates more stable land for farming. Berms are useful tools for separating areas of the garden into distinct categories (for example, planting beds). They also help drain water away from your house and allow it to flow through rather than onto your patio or driveway. This helps avoid problems with flooding or mud slides.