20th century. Major conservation work has taken place since then to reverse the effects of London's air pollution, and extensive repairs followed the Second World War, including the simplified reconstruction of the Commons Chamber following its bombing in 1941. The Palace is one of the centres of political life in the United Kingdom; "Westminster" has become a metonym for the UK Parliament and the British Government, and the Westminster system of government commemorates the name of the palace. The Elizabeth Tower, in particular, often referred to by the name of its main bell, Big Ben, has become an iconic landmark of London and of the United Kingdom in general, one of the most popular tourist attractions in the city, and an emblem of parliamentary democracy. Tsar Nicholas I of Russia called the new palace "a dream in stone". The Palace of Westminster has been a Grade I listed building since 1970 and part of a UNESCO World Heritage Site since 1987. History Old Palace The site of the Palace of Westminster was strategically important during the Middle Ages, as it was located on the banks of the River Thames. Known in medieval times as Thorney Island, the site may have been first-used for a royal residence by Canute the Great during his reign from 1016 to 1035. St Edward the Confessor, the penultimate Anglo-Saxon monarch of England, built a royal palace on Thorney Island just west of the City of London at about the same time as he built (1045–1050) Westminster Abbey. Thorney Island and the surrounding area soon became known as Westminster (from the words west and minster). Neither the buildings used by the Anglo-Saxons nor those used by William I () survive. The oldest existing part of the Palace (Westminster Hall) dates from the reign of William I's successor, King William II (). The Palace of Westminster functioned as the English monarchs' principal residence in the late Medieval period. The predecessors of Parliament, the Witenagemot and the Curia Regis, met in Westminster Hall (although they followed the King when he moved to other palaces). Simon de Montfort's Parliament, the first to include representatives of the major towns, met at the Palace in 1265. The "Model Parliament", the first official Parliament of England, met there in 1295, and almost all subsequent English Parliaments and then, after 1707, all British Parliaments have met at the Palace. In 1512, during the