They are primarily distinguished by their size, carrying a larger cross-section of water than most water-supply aqueducts.Roman aqueducts were used to transport water and were created in Ancient Rome.Early aqueducts such as the three on the Canal du Midi had stone or brick arches, the longest span being 18.3 metres (60 ft) on the Cesse Aqueduct, built in 1690.But, the weight of the construction to support the trough with the clay or other lining to make it waterproof made these structures clumsy.Within ten years Telford had completed the far more ambitious Pontcysyllte Aqueduct in Wales on the Llangollen Canal over the River Dee valley, with a total length 307 metres and a height of 38 metres, making it the tallest navigable aqueduct in the world.