Ely (/ˈiːli/ EE-lee) is a cathedral city in Cambridgeshire, England, about 14 miles (23 km) north-northeast of Cambridge and about 80 miles (129 km) by road from London. Ely is built on a 23-square-mile (60 km2) Kimmeridge Clay island which, at 85 feet (26 m), is the highest land in the Fens. It was due to this topography that Ely was not waterlogged like the surrounding Fenland, and was an island separated from the mainland. Major rivers including the Witham, Welland, Nene and Great Ouse feed into the Fens and, until draining commenced in the eighteenth century, formed freshwater marshes and meres within which peat was laid down. Once the Fens were drained, this peat created a rich and fertile soil ideal for farming.