Bristol is a city, ceremonial county and unitary authority in England. It lies within a limestone area from the Mendip Hills in the south to the Cotswolds in the northeast. the Avon Gorge was formed by glacial meltwater after the last ice age and cuts through the limestone. The limestone was quarried to build the city, which protected the surrounding land from development. The result are multiple open cast and underground quarries and natural caves which were discovered during quarrying.