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Mechanical gearing: from 350 BC

An important adaptation of the wheel in technology is the pulley - a wheel round which a rope is run to exert force on an object at the other end. Such a machine is first mentioned in a Greek text of the 4th century BC, but it is likely to have been known much earlier.

In the simplest pulley a single wheel is used (as in hauling a flag up a flagpole). But major mechanical advantages can be achieved with two or more wheels - making it possible to lift a heavier object, albeit more slowly. The effect of two pulleys is that a force capable of pulling the rope two yards at one end will exert twice that force over a distance of only one yard at the other. The effect increases dramatically the more pulleys there are.

A closely related mechanical principle for lifting is the lever, where a non-central fulcrum means that a weak force exerted at one end of a rigid bar becomes a stronger force over a shorter distance at the other end. This discovery is often linked with Greek science, because of the legendary remark attributed to Archimedes in the 3rd century BC: 'Give me a fulcrum and I will move the earth.'

In fact the lever has much earlier origins. It is probably the first mechanical device used in technology. From about 3000 BC the principle is put to practical use in both Egypt and Mesopotamia.

Another important mechanical principle, that of the screw, is also commonly associated with Archimedes. The concept may have been discovered much earlier in Egypt, or by Greeks before the time of Archimedes. But as a system of raising water, the screw has long been linked with his name.

A different application, the screw press, is developed in Mediterranean regions at some time before the 1st century AD. Considerable pressure is needed to extract oil from olives. In earlier presses this is achieved by a heavy beam, on a lever principle. But a screw is more relentlessly effective, increasing the pressure to a new level with each turn.

Rotary power: c.200 BC

The turning of a drum by pressure on projecting arms (the principle of the capstan or windlass) is a necessary part of any rotary machine, such as a screw press. The same principle makes it possible to grind corn between millstones.

The manual grinding of grain, together with the baking of bread, go back at least 8000 years to settled communities such as Catal Huyuk. Early forms of grinding involve rubbing one hard surface against another by hand (the pestle and mortar is one such method). Rotary mills, turned by slaves or animals, are known from at least the 2nd century BC.

Millstones: 2nd century BC

The milling of grain into flour, previously done by hand on a rough flat stone, achieves a major technological advance with the introduction of heavy stones which grind against each other to crush the seeds between them. The first mention of such stones is by a Roman author of the 2nd century BC, and many have been found at Pompeii.

The bottom stone is flat and circular, like a cheese, but the top one is tall and waisted - with a hole through it for grain to trickle down to the grinding surface. The upper stone is turned by pressure against wooden posts set into its waisted centre. Mills of this kind, when driven by asses or horses, are the first industrial use of animal power.

Water mills: 1st century BC

The emergence of the water mill is too gradual to be pinpointed. It is perhaps a development of a different form of water wheel. Once rotary power is available, a simple gear will transfer it to the shaft or axle of a wheel. And a vertical wheel, with jugs attached to its rim, will perform the useful function of raising water by scooping it up at the bottom and pouring it out at the top.

Such water wheels, worked by oxen or camels, are in use in many parts of the world even today. They may well have been the distant inspiration of the water mill, where the process is reversed - the wheel itself being turned by water, and the power transferred in the other direction along the axle.

In an even simpler version of a water mill, a horizontal water wheel in a stream can turn a millstone above by means of a fixed shaft. Water mills of one kind or the other are certainly known by the 1st century BC in the Hellenistic world. A poem of the time advises young girls that they can now let the nymphs of the stream do the hard work of milling.

The Romans adopt the Greek water mill, and Vitruvius in the 1st century BC gives the first written account of a geared water wheel. But the Romans do not apply the principle widely. The widespread and effective use of water power will be a technological achievement of the Middle Ages.

Cement: c.200 BC

Builders in Greek cities on the coast of Turkey (and in particular Pergamum) evolve cement in about 200 BC as a structural material, in place of weaker mortars such as gypsum plaster (used in Egypt) or bitumen (in Mesopotamia). The secret of the new material is the lime which binds sand, water and clay.

The Romans subsequently use finely ground volcanic lava in place of clay, deriving it mainly from the region of Pozzuoli. Their cement, known for this reason as pozzolanic, is the strongest mortar in history until the development of Portland cement. When small fragments of volcanic rubble are included, the result is concrete - making possible the great arches and aqueducts of Roman architecture, and playing its part in Roman roads.

Roman roads: 2nd century BC - 2nd century AD

The great network of Roman roads, the arterial system of the empire, is constructed largely by the soldiers of the legions, often with the assistance of prisoners of war or slave labour. The amount of labour involved is vast, for these highways are elaborate technological undertakings.

The average width of a Roman road is about 10 yards. Below the paved surface the fabric extends to a depth of 4 or 5 feet in a succession of carefully constructed layers.

First a trench is excavated. Its bottom is rammed hard, and if necessary is strengthened by driving in piles. Then four successive layers are constructed, each a foot or more thick. The first is of masonry, laid in cement or clay. Above this is a course of concrete, then gravel and cement. Finally the top layer is laid in dressed stones, sloping away in a pronounced camber from the centre.

The designers of the Roman roads are single-minded. Paying scant attention to the demands of contours, and having few property rights to consider, their mission is to drive the road straight ahead. The legions will march far in the empire, but they will take the shortest route.

Part of the purpose of the Roman roads is speed of communication, so there are posthouses with fresh horses every 10 miles along the route and lodgings for travellers every 25 miles. By the 2nd century AD the network spreads all round the Mediterranean and throughout Europe up to the Danube, the Rhine and northern England, amounting in all to some 50,000 miles. This far outdoes even the very impressive achievement of the Persian roads . Travellers on foot or horseback have rarely been so well provided for.

For haulage purposes these roads are less satisfactory, because the straight line results in some very steep hills. Anyone with a wagon and horse would prefer an attitude less severe than that of the Roman road engineer.

Arch, vault and dome: from the 1st century BC

The greatest achievement of Roman architecture and technology lies in the development of these three architectural forms. The dome has long been a familiar concept (appearing dramatically in the passage grave on the Île Longue or in the tholos at Mycenae), but nothing has been made of it in the major architectural traditions. The spectacular temples of Egypt or Greece are exclusively trabeate, using flat horizontal lintels to span open spaces.

The arch has far greater capabilities than the lintel, for it can combine many smaller units (of stone or brick) to make a greater whole. In Greek architecture a single vast stone lintel can reach between columns at most 7 yards apart. A Roman brick arch can span 50 yards.

The arch, the vault and the dome are all applications of the same concept. The vault, or open-ended tunnel, is only an exceptionally deep arch. The dome is in effect a collection of arches all sharing the same centre. In each case the pressure of gravity on the material forming the arch will hold it together as long as the outward thrust is contained by buttresses.

The Roman achievement in all these forms is greatly assisted by their development of concrete. An arch or dome bonded into solid form by a strong inner layer of concrete sits as one unit, exerting its weight downwards rather than outwards. This makes possible such miracles as the 1st-century Pont du Gard or the 2nd-century dome of the Pantheon.

The Pont du Gard: AD c.20

The scale of Roman architectural ambition is superbly seen in the great aqueduct at Nîmes, known as the Pont du Gard ('bridge of the Gard'). Constructed in about AD 20, this gigantic structure is purely practical. It is a section of a channel bringing water from the river Eure to the new Roman town of Nîmes.

The water flows gently downhill for a distance of almost 50 km. The Pont du Gard, with its three towering tiers of arches, carries it over the deep valley of the river Gard - in itself a source of water nearer to Nîmes, but too low-lying to reach the town by gravity.

Roman bridges: 1st - 2nd century AD

Bridges are as much part of the Roman architectural achievement as aqueducts, and they present even greater constructional problems.

Some of the most impressive Roman bridges are over ravines. A fine surviving example, built for Trajan in AD 105, spans the Tagus in Spain, at Alcántara. Its two massive central arches, 110 feet wide and 210 feet above the normal level of the river, are made of uncemented granite. Each wedge-shaped block weighs 8 tons. During construction these blocks are winched into place by a system of pulleys, powered perhaps by slave labour on a treadmill. They are supported on a huge timber structure standing on the rocks below - to be removed when the arch is complete.

An equally remarkable feat of Roman construction is the building of bridges across rivers where no rock or island emerges from the water to carry the piers. An example survives in Rome - the Sant'Angelo bridge, built for Hadrian in AD 134 as an approach to his great circular mausoleum, now the Castel Sant'Angelo.

The building of such bridges is made possible by the Roman perfection of cement and concrete, and by their invention of the cofferdam.

Roman cofferdams: 2nd century AD

A cofferdam is a watertight sheath within which the foundation of a bridge can be constructed in the bed of a river. The Roman pioneers of this technology drive two circles of wooden piles into the river and then pack the space between them with clay to achieve the watertight seal. The water and the mud of the river bed are scooped out of the resulting cylinder so that a concrete foundation for the pier can be constructed on firm ground.

The arches of the Sant'Angelo bridge still stand on foundations created in the Tiber in this way nearly 1900 years ago.

Hero's dioptra: 1st century AD

One of the surviving books of Hero of Alexandria, entitled On the Dioptra, describes a sophisticated technique which he has developed for the surveying of land. Plotting the relative position of features in a landscape, essential for any accurate map, is a more complex task than simply measuring distances.

It is necessary to discover accurate angles in both the horizontal and vertical planes. To make this possible a surveying instrument must somehow maintain both planes consistently in different places, so as to take readings of the deviation in each plane between one location and another.

This is what Hero achieves with the instrument mentioned in his title, the dioptra - meaning, approximately, the 'spyhole' through which the surveyor looks when pinpointing the target in order to read the angles.

Hero adapts, for this new and dificult task, an instrument long used by Greek astronomers (such as Hipparchus) for measuring the angle of stars in the sky. It is evident from his description that the dioptra differs from the modern theodolite in only two important respects. It lacks the added convenience of two inventions not available to Hero - the compass and the telescope.

Knitting: from the 3rd century AD

Knitting, as a concept, is very simple but extremely hard to imagine. It is likely, therefore, to be one of the few technological developments in ancient history to have an actual inventor. As a challenge to the inventive mind, the problem ('Transform a continuous thread into a piece of fabric without at any point cutting the thread') still seems difficult.

The likelihood of a single moment of invention is also made more probable by the late arrival of knitting. Even though it makes no technological demands (neolithic communities could provide a skein of wool and two long needles), civlization is 3000 years old before the first row is knitted.

Knitting first appears in the Roman empire, in the 3rd century AD. The earliest examples to survive are socks (found in tombs in Egypt), and it is in footwear that the advantages of the new technology are most obvious.

Until this time feet have usually been kept warm and protected within the shoe by wrapping them in strips of cloth or leather. In the 2nd century AD the Romans evolve a tailored sock, made of pieces of cloth sewn together. But these lack the elasticity of a knitted fabric. Eventually the demand for knitted stockings is so great that the first knitting machine, devised in 1589, is an early landmark of the Industrial Revolution.

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