Little is known of London prior to A.D. 61, when, as recorded by the Roman historian Tacitus, the followers of Queen Boadicea rebelled and slaughtered the inhabitants of the Roman fort Londinium. Roman authority was soon restored, and the first city walls were built, remnants of which still exist. After the final withdrawal of the Roman legions in the 5th cent., London was lost in obscurity. Celts, Saxons, and Danes contested the general area, and it was not until 886 that London again emerged as an important town under King Alfred, who rebuilt the defenses against the Danes and gave the city a government.
London put up some resistance to William I in 1066, but he subsequently treated the city well. During his reign the White Tower, the nucleus of the Tower of London, was built just east of the city wall. Under the Normans and Plantagenets (see Great Britain), the city grew commercially and politically and during the reign of Richard I (1189–99) obtained a form of municipal government from which the modern City Corporation developed. In 1215, King John granted the city the right to elect a mayor annually.
The guilds of the Middle Ages gained control of civic affairs and grew sufficiently strong to restrict trade to freemen of the city. The guilds survive today in 80 livery companies, of which members were once the voters in London's municipal elections. Medieval London saw the foundation of the Inns of Court and the construction of Westminster Abbey. By the 14th cent. London had become the political capital of England. It played no active role in the Wars of the Roses (15th cent.).
The reign of Elizabeth I brought London to a level of great wealth, power, and influence as the undisputed center of England's Renaissance culture. This was the time of Shakespeare (and the Globe Theatre) and the beginnings of overseas trading companies such as the Muscovy Company. With the advent (1603) of the Stuarts to the throne, the city became involved in struggles with the crown on behalf of its democratic privileges, culminating in the English civil war.
In 1665, the great plague took some 75,000 lives. A great fire in Sept., 1666, lasted five days and virtually destroyed the city. Sir Christopher Wren played a large role in rebuilding the city. He designed more than 51 churches, notably the rebuilt St. Paul's Cathedral. Other notable churches include the gothic Southwark Cathedral, St. Paul's Church (1633; designed by Inigo Jones), St. Martin-in-the-Fields (18th cent.), and Westminster Cathedral. Much of the business of London as well as literary and political discussion was transacted in coffeehouses, forerunners of the modern club. Until 1750, when Westminster Bridge was opened, London Bridge, first built in the 10th cent., was the only bridge to span the Thames. Since the 18th cent., several other bridges have been constructed; the Tower Bridge was completed in 1894.
In the 19th cent., London began a period of extraordinary growth. The area of present-day Greater London had about 1.1 million people in 1801; by 1851, the population had increased to 2.7 million, and by 1901 to 6.6 million. During the Victorian era, London acquired tremendous prestige as the capital of the British Empire and as a cultural and intellectual center. Britain's free political institutions and intellectual atmosphere made London a haven for persons unsafe in their own countries. The Italian Giuseppe Mazzini, the Russian Aleksandr Herzen, and the German Karl Marx were among many politically controversial figures who lived for long periods in London.
Many buildings of central London were destroyed or damaged in air raids during World War II. These include the Guildhall (scene of the lord mayor's banquets and other public functions); No. 10 Downing Street, the prime minister's residence; the Inns of Court; Westminster Hall and the Houses of Parliament; St. George's Cathedral; and many of the great halls of the ancient livery companies. Today there are numerous blocks of new office buildings and districts of apartment dwellings constructed by government authorities. The growth of London in the 20th cent. has been extensively planned. One notable feature has been the concept of a "Green Belt" to save certain areas from intensive urban development. In 1982, a tax-free zone in the Docklands in the East End's Tower Hamlets borough was created to stimulate development. Although the Canary Wharf financial center (with Lloyd's futuristic building, opened in 1986) was initially slow to fill, it now rivals the City.
London has an ethnically and culturally diverse population, with large groups of immigrants from Commonwealth nations. South Asian, West Indian, African, and Middle Eastern peoples account for much of the immigrant population. The city is the site of one of the largest Hindu temple complexes and the largest Sikh temple outside India; there also are many mosques, including one of the largest in Europe. With the reestablishment of the city's central government (2000), London built its egg-shaped City Hall (2002), on the south bank of the Thames opposite the Tower of London. The city was the site of the 1908, 1948, and 2012 summer Olympic games.