Roman Engineering - Power Technology

Power Technology

Water wheel technology was developed to a high level during the Roman period, a fact attested by Vitruvius and Pliny the Elder in De Architectura and Naturalis Historia respectively. The largest complex of water wheels existed at Barbegal near Arles, where the site was fed by a channel from the main aqueduct feeding the town. It is estimated that the site comprised 16 separate overshot water wheels arranged in two parallel lines down the hillside. The outflow from one wheel became the input to the next one down in the sequence.

Twelve kilometers north of Arles, at Barbegal, near Fontvieille, where the aqueduct arrived at a steep hill, the aqueduct fed a series of parallel water wheels to power a flourmill. There are two aqueducts which join just north of the mill complex, and a sluice which enabled the operators to control the water supply to the complex. There are substantial masonry remains of the water channels and foundations of the individual mills, together with a staircase rising up the hill upon which the mills are built. The mills apparently operated from the end of the 1st century until about the end of the 3rd century. The capacity of the mills has been estimated at 4.5 tons of flour per day, sufficient to supply enough bread for the 12,500 inhabitants occupying the town of Arelate at that time.

The Hierapolis sawmill was a Roman water-powered stone saw mill at Hierapolis, Asia Minor (modern-day Turkey). Dating to the second half of the 3rd century AD, the sawmill is the earliest known machine to combine a crank with a connecting rod.

The watermill is shown on a raised relief on the sarcophagus of Marcus Aurelius Ammianos, a local miller. A waterwheel fed by a mill race is shown powering two frame saws via a gear train cutting rectangular blocks.

Further crank and connecting rod mechanisms, without gear train, are archaeologically attested for the 6th century AD water-powered stone sawmills at Gerasa, Jordan, and Ephesus, Turkey. Literary references to water-powered marble saws in Trier, now Germany, can be found in Ausonius' late 4th century AD poem Mosella. They attest a diversified use of water-power in many parts of the Roman Empire.

A complex of mills also existed on the Janiculum in Rome fed by the Aqua Traiana. The Aurelian Walls were carried up the hill apparently to include the water mills used to grind grain towards providing bread flour for the city. The mill was thus probably built at the same time as or before the walls were built by the emperor Aurelian (reigned 270-275 AD). The mills were supplied from an aqueduct, where it plunged down a steep hill.

The site thus resembles Barbegal, although excavations in the late 1990s suggest that they may have been undershot rather than overshot in design. The mills were in use in 537 AD when the Goths besieging the city cut off their water supply. However they were subsequently restored and may have remained in operation until at least the time of Pope Gregory IV (827-44).

Many other sites are reported from across the Roman Empire, although many remain unexcavated.