London is not characterized by any particular architectural style, having accumulated its buildings over a long period of time. Few structures predate the Great Fire of 1666, notable exceptions including the Tower of London, Westminster Abbey, Banqueting House and several scattered Tudor survivors in the City of London.
In itself, the City contains a wide variety of styles, progressing through Wren's late 17th-century churches and the financial institutions of the 18th and 19th century such as the Royal Exchange and the Bank of England, to the early 20th century Old Bailey (England and Wales' central criminal court) and the 1960s Barbican Estate. Notable recent buildings are the 1980s skyscraper Tower 42, the Lloyd's building with services running along the outside of the structure, and the 2004 Swiss Re building, known as the "Gherkin". (from Wikipedia)