City of London tall office buildings including the 600-foot (183 m), 47-storey Natwest Tower, the first skyscraper in the UK. Office space development has intensified especially in the central, northern and eastern parts, with skyscrapers including 30 St. Mary Axe ("the Gherkin"'), Leadenhall Building ("the Cheesegrater"), 20 Fenchurch Street ("the Walkie-Talkie"), the Broadgate Tower and the Heron Tower, the tallest in the City. Another skyscraper, 22 Bishopsgate, is under construction. The main residential section of the City today is the Barbican Estate, constructed between 1965 and 1976. The Museum of London is based there, as are a number of other services provided by
30 St Mary Axe designed by Norman Foster and Arup Group. It was erected by Skanska; construction started in 2001. The building has become a recognisable feature of London, and it is one of the city's most widely recognised examples of contemporary architecture. The building stands on the former sites of the Baltic Exchange (24-28 St Mary Axe), which was the headquarters of a global marketplace for shipping freight contracts and also soft commodities, and the Chamber of Shipping (30-32 St Mary Axe). On 10 April 1992, the Provisional IRA detonated a bomb close to the Exchange, causing extensive damage to the historic building