The cathedral is built from stone quarried from Barnack in Northamptonshire (bought from Peterborough Abbey, whose lands included the quarries, for 8000 eels a year), with decorative elements carved from Purbeck Marble and local clunch. The plan of the building is cruciform (cross-shaped), with an additional transept at the western end. The total length is 537 feet (164 m), and the nave at over 75 m (246 ft) long remains one of the longest in Britain. The west tower is 66 m (217 ft) high. The unique Octagon 'Lantern Tower' is 23 m (75 ft) wide and is 52 m (171 ft) high. Internally, from the floor to the central roof boss the lantern is 43 m (141 ft) high. It is known locally as "the ship of the Fens", because of its prominent position above the surrounding flat landscape.