The Mustang is a small, hardy wild horse descended from Arabian horses brought to America by Spanish explorers. The name Mustang comes from the Spanish word mesteño or mestengo meaning wild or stray. With time, the wild herds of Mustangs increased in numbers and became favorite mounts for the Indians. Mustang horses were used as cow ponies and later were replaced by better quality breeds. Their number has declined as a result. They still roam the wild western plains and are now protected by law. The Mustang Horse contributed to formation of many American breeds.