A crane is a machine that is capable of raising and lowering heavy objects and moving them horizontally. Cranes are distinguished from hoists, which can lift objects but that cannot move them sideways. Cranes are also distinguished from conveyors, which lift and move bulk materials, such as grain and coal, in a continuous process. The word crane is taken from the fact that these machines have a shape similar to that of the tall, long-necked bird of the same name.
As early as the first century, cranes were built that were powered by human beings or animals operating a treadmill or large wheel. These early cranes consisted of a long wooden beam, known as a boom, connected to a rotating base. The wheel or treadmill powered a drum, around which a rope was wound. The rope was connected to a pulley at the top of the boom and to a hook that lifted the weight.
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