Crane (machine)

A crane is a machine that lifts and moves heavy objects both up and down and side to side, using a boom, hoist, wire ropes or chains, and sheaves. It relies on simple machines like levers and pulleys to gain mechanical advantage. Cranes are widely used in transportation for loading and unloading cargo, in construction for shifting materials, and in manufacturing for putting together large equipment.

The earliest known crane-like device was the shaduf, a water-lifting tool invented in ancient Mesopotamia (modern Iraq) and later used in ancient Egypt. Construction cranes appeared in ancient Greece, powered by people or animals like donkeys, and were used to build structures.

The Romans later developed larger cranes with human-powered treadwheels, allowing heavier loads to be lifted. During the High Middle Ages, harbor cranes were built to load and unload ships and assist in shipbuilding—some were set into stone towers for extra strength. Early cranes were made of wood, but cast iron, iron, and steel became common after the Industrial Revolution.

For centuries, cranes were powered by human or animal effort, though watermills and windmills could drive hoists using natural power. The first mechanical power came from steam engines, with the earliest steam crane appearing in the 18th or 19th century; many remained in use into the late 20th century. Modern cranes typically use internal combustion engines, electric motors, or hydraulic systems for much greater lifting capacity, though manual cranes are still used where power is too costly.

Cranes come in many types for specific tasks. Sizes range from small jib cranes in workshops to tall tower cranes for high buildings.

Mini-cranes also help construct tall buildings by reaching tight spaces. Large floating cranes are used to build oil rigs and salvage sunken ships. Some lifting machines, like stacker cranes and loader cranes, are commonly called cranes even if they don't strictly fit the definition.

Ancient civilizations

The name "crane" comes from the bird's long neck, similar to the Greek geranos and French grue. The earliest known lifting device, the shaduf, was used in Mesopotamia around 3000 BCE for irrigation. It later appeared in Egypt around 2000 BCE. The shift to building cranes happened in ancient Greece in the late 6th century BCE.

Evidence from stone blocks of Greek temples—cutting marks for lifting tongs and Lewis irons—shows cranes were used. These marks appear above the block's center of gravity or in pairs, confirming the use of lifting devices. This need for mechanical advantage led to winches and pulleys, replacing labor-intensive ramps.

Unlike earlier large blocks, classical Greek temples like the Parthenon used stones weighing under 15–20 metric tons, and monolithic columns were replaced by stacked drums. The exact reason for switching from ramps to cranes is unclear, but it may be that Greece's unstable politics favored small, skilled teams over large, unskilled labor. The first clear written evidence of a compound pulley system appears in the Mechanical Problems attributed to Aristotle (384–322 BC). Around that time, Greek temple block sizes grew again, suggesting the compound pulley had reached construction sites.

Roman Empire

Cranes reached their peak in ancient times during the Roman Empire, when building boomed and structures grew enormous. The Romans improved on Greek designs, and detailed accounts survive from engineers Vitruvius and Heron of Alexandria. Two reliefs of Roman treadwheel cranes exist, notably the Haterii tombstone from the late first century AD.

Roman engineers calculated mechanical advantage ratios. The simplest Roman crane, the trispastos, had a double-beam jib, a winch, a rope, and a block with three pulleys. With a 3:1 mechanical advantage, a single man working the winch could lift about 150 kg, assuming a person can exert 50 kg over time.