Arranging mills on a slope
Barbegal stood near Roman Arelate, present-day Arles. Builders used the slope’s elevation difference to arrange sixteen mills in two rows of eight. Central buildings separated the rows, and an aqueduct entered above them, bringing water supply and mechanical production together at one site.
Water passed from an upstream basin to the next wheel, continuing downhill along each row. This arrangement allowed the same water to perform work at successive heights. A channel previously supplying the city was diverted during the second century to the new mills, while other adjusted channels supplied the city.
How water turned millstones
Vitruvius described the basic transmission of a watermill in The Ten Books on Architecture: flowing water turned a wheel and its axle, whose toothed wheel engaged another to drive the millstone. Grain entered from a hopper above and was ground by the revolving stones. His account connected water flow with the mechanical steps of grain processing.
Barbegal concentrated water-powered milling in a complex of machines. Supplying water above the wheels suited the steep slope and successive basins. Flowing water provided part of the power otherwise supplied by people or animals, connecting milling work with channel discharge and the condition of axles and stones.
Keeping the next wheel turning
Serial mills required more than the design of one wheel. Starting or stopping an upstream machine changed the water reaching those below, while small basins constrained the placement of flumes. Researchers identified the shape of a bent wooden flume in carbonate fragments and combined it with hydraulic calculations to reconstruct a supply arrangement for overshot wheels.
The reconstructed flume first descended, then delivered water to the wheel through a more nearly level outlet section. Researchers proposed that this arrangement adjusted outlet velocity within tight confines and reduced fluctuations caused by upstream operation. Slope, flumes and basins jointly affected continued operation, making small design decisions important to the whole row.
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After the wood disappeared
The wooden machinery has decayed, while stone structures remain. Water flowing over flumes and wheels deposited calcium carbonate as a hard crust against the timber. Some surviving crusts retain wood grain and structural shapes, providing evidence from which the machines can be reconstructed.
Barbegal directly combined food processing and water engineering: spring water traveled through channels, wheels connected to transmissions, and grain passed through stones. Large-scale milling required these operations to work together. Its remains allow power, construction and maintenance in ancient food production to be studied as connected activities.