At the east end of the Binnenhof's central courtyard, the 13th-century Knights' Hall (Ridderzaal) is a spectacular historic building still used for state receptions and the opening of parliament each September. This large Gothic hall - it measures 40 meters by 20 meters - boasts many magnificent stained-glass windows depicting the coats of arms of Dutch towns, as well as the spectacular Rose Window with the arms of the principal noble families of the Netherlands. The heavy timber roof structure with its 18-meter-long beams has the appearance of an upturned ship, and carved wooden heads symbolizing eavesdroppers from the "higher powers" are supposed to deter members of the assembly from lying. Originally built as a banqueting hall, it later served as a market, promenade, drill hall, playground, and even a hospital before being restored in 1904.