How Roman Water Flowed Uphill Without a Single Pump
Where a valley was too deep to bridge, Roman engineers sent water down one side and let its own weight push it back up the other.
Quick Context
Everyone photographs the arches. But where a valley was too deep to bridge, Roman engineers did something that sounds impossible: they sent the water down one side in a sealed pipe and let its own weight push it back up the other. There were no pumps, just gravity and a lot of pressure: about four atmospheres at the bottom of the siphon at Aspendos, in southern Turkey, where two of the towers that carried it still stand roughly 30 m tall.
At Lugdunum, today’s Lyon, the Gier aqueduct needed four siphons, and the deepest plunged more than 120 m into its valley before climbing back out. The Romans thought hard about materials, too. Vitruvius, the architect who wrote down the recipe for concrete that grew stronger in seawater, warned that water piped through lead was unhealthy and recommended clay.
