An aqueduct is an engineered structure — typically a bridge or elevated channel — designed to transport water across a valley, river, road or other obstacle, using gravity to maintain a continuous flow.
The word comes from the Latin aqua (water) and ducere (to lead). Although most closely associated with ancient Rome, aqueducts have been built by many civilisations and remain relevant in modern water engineering.
Roman aqueducts
The Romans were the most prolific aqueduct builders of the ancient world. Over a period of about 500 years they constructed hundreds of aqueducts to supply cities, baths, fountains and industrial sites across the empire. Key engineering principles included:
- Gravity flow — Roman aqueducts relied on a carefully maintained gradient, typically between 1:500 and 1:5000, to keep water moving without pumps.
- Covered channels — most of the route ran in covered stone or concrete channels at ground level or in shallow tunnels, protecting the water from contamination and evaporation.
- Arcade bridges — where the channel had to cross a valley, the Romans built multi-tiered stone arched bridges to maintain the gradient. The Pont du Gard in southern France (three tiers, 49 metres high) and the Aqueduct of Segovia in Spain are the best-preserved examples.
Modern aqueducts
Today, the term aqueduct is used for large-scale water conveyance systems. Modern aqueducts may take the form of pressurised pipelines, open canals, tunnels or bridge structures. Examples include the California Aqueduct (over 700 kilometres) and the Thirlmere Aqueduct in England.
Modern aqueduct bridges are built in reinforced concrete or steel and may carry pipes or open channels across rivers, motorways and railways.
Canal aqueducts
In inland navigation, an aqueduct is a bridge that carries a navigable canal over a valley or river. Notable examples include the Pontcysyllte Aqueduct in Wales (a UNESCO World Heritage Site) and the Magdeburg Water Bridge in Germany.
Related terms
- Gravity water supply
- Arcade bridge
- Water conveyance
- Siphon (inverted siphon)