The Gallery Tower originally guarded the 152-metre (499-foot) long, narrow walled-causeway that still runs from the Brays to the main castle.[6] This causeway was called the Tiltyard, as it was used for tilting, or jousting, in medieval times. The Tiltyard causeway acted both as a dam and as part of the barbican defences.[2] To the east of the Tiltyard is a lower area of marshy ground, originally flooded and called the Lower Pool, and to the west an area once called the Great Mere. The Great Mere has been drained and cultivated as a meadow, but it was originally a large lake covering around 100 acres (40 ha), dammed by the Tiltyard causeway.[7]