A train is a set of vehicles on wheels that moves with the help of a locomotive or any other tractor. It is an integral part of the railway - the track along which trains pass. Railways in one form or another were used long before the appearance of the first steam locomotive. The earliest trains used human force to push or pull them along the tracks. Horses were stronger than humans and could pull heavier loads. But it was the invention of the steam locomotive that led to the potential of the railway system being fully appreciated.