Once part of the city defences and closed at night, its guard houses used to display the heads of traitors, such as Thomas More (1535), impaled upon pikes. Rebuilt in granite in 1831 by John Rennie, London Bridge was dismantled again in 1969 because it was too narrow. It was then sold to Americans buyers who rebuilt it in Arizona. The present bridge, finished in 1973, is the most modern in London.