The word ambulance comes from the Latin word ambulare, meaning to walk about. Ambulances originally referred to mobile medical structures that could be easily walked from one location to another by an army during a war. These were also called field hospitals. Eventually, horses and wagons were used to transport sick or injured people or medical supplies to medical facilities. In some developing countries, ambulances are still wagons, though buses are also used. Boats and even bicycles may be used as ambulances when the ill or injured are located in remote areas.