The city of Nottingham in Nottinghamshire, England, is spread over a soft sandstone ridge which forms low hills to the north of the River Trent. This sandstone rock, formed some 230 million years ago, has high strength, and yet soft enough to be worked with chisels and hand-held picks. This unusual dual quality of strength and softness allows the rock to be easily excavated and still stand safely over unsupported spans. Nottingham’s earliest inhabitants exploited this peculiar property. They found that it was easier and cheaper to create dwelling space by excavating into the foot of the sandstone cliffs along the edge of the Trent floodplain, than build houses above ground. Indeed, Nottingham was once known in the Brythonic language as Tigguo Cobauc, meaning “Place of Caves”, and was referred to as such by the Bishop of Sherborne Asser in the 9th century.