Pair and spare dating

The first known construction cranes were invented by the Ancient Greeks and were powered by men or beasts of burden, such as donkeys.These cranes were used for the construction of tall buildings.Some lifting machines do not strictly fit the above definition of a crane, but are generally known as cranes, such as stacker cranes and loader cranes.The archaeological record shows that no later than c.515 BC distinctive cuttings for both lifting tongs and lewis irons begin to appear on stone blocks of Greek temples.

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In contrast to the archaic period with its tendency to ever-increasing block sizes, Greek temples of the classical age like the Parthenon invariably featured stone blocks weighing less than 15-20 metric tons.The Romans adopted the Greek crane and developed it further.We are relatively well informed about their lifting techniques, thanks to rather lengthy accounts by the engineers Vitruvius (De Architectura 10.2, 1-10) and Heron of Alexandria (Mechanica 3.2-5).Since these holes point at the use of a lifting device, and since they are to be found either above the center of gravity of the block, or in pairs equidistant from a point over the center of gravity, they are regarded by archaeologists as the positive evidence required for the existence of the crane.The introduction of the winch and pulley hoist soon lead to a widespread replacement of ramps as the main means of vertical motion.Larger cranes were later developed, employing the use of human treadwheels, permitting the lifting of heavier weights.In the High Middle Ages, harbour cranes were introduced to load and unload ships and assist with their construction – some were built into stone towers for extra strength and stability.The polyspastos, when worked by four men at both sides of the winch, could readily lift 3,000 kg (3 ropes x 5 pulleys x 4 men x 50 kg = 3,000 kg).If the winch was replaced by a treadwheel, the maximum load could be doubled to 6,000 kg at only half the crew, since the treadwheel possesses a much bigger mechanical advantage due to its larger diameter.At the temple of Jupiter at Baalbek, for instance, the architrave blocks weigh up to 60 tons each, and one corner cornice block even over 100 tons, all of them raised to a height of about 19 m.It is assumed that Roman engineers lifted these extraordinary weights by two measures (see picture below for comparable Renaissance technique): First, as suggested by Heron, a lifting tower was set up, whose four masts were arranged in the shape of a quadrangle with parallel sides, not unlike a siege tower, but with the column in the middle of the structure (Mechanica 3.5).

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