Who constructed the oldest canal?

Canals were introduced during the Roman occupation of the south of Great Britain, and were used mainly for irrigation. However, the Romans did create several navigable canals, such as the Foss Dyke.

The Bridgewater Canal, can claim to be the first modern artificial canal in Britain, opened in 1761 to carry coal.
Designed by James Brindley, and built for Francis Egerton, 3rd Duke of Bridgewater.