A train is a set of cars on a railway. The vehicles that carry freight are called "cars" (in the United States) or "wagons" (in the United Kingdom). The ones that carry passengers are often called coaches or carriages. A place where a train stops to let people get on and off is called a Train station or railway station. Early trains used horse power and ran on wooden or iron tracks. These were used in the Middle Ages. The first steam trains were built in England in the early 19th century. Long before railways, "train" meant any group of vehicles or pack animals traveling in a line, as in wagon train or camel train.