How do you celebrate the start of mankind's third millennium – two thousand years of history? In the UK, the decision was made to build a huge domed structure at Greenwich – the prime meridian at zero degrees longitude – on 300 acres of polluted and derelict industrial land. Construction began in 1997 and was completed in time for the Millennium celebrations. The Millennium Dome (re-branded in 2005 as the O2 Arena) in London is a unique building: an engineering marvel and the world's largest single roofed structure. It is one of the most easily recognised and controversial landmarks in London and is a deceptively simple tensioned cable net structure, similar to a suspension bridge, with a roof of weather-resistant plastic strong enough to carry the weight of a jumbo jet, although the roof structure weighs less than the air contained within the building. The Dome has a diameter of 365 metres, a circumference of 1kilometre and a ground floor area of 80,000 square metres. It is 50 metres high at the central point, each of the 12 yellow masts are 100 metres high and it’s supported by 70 kilometres of tensioned steel cable. The fabric cover is made of PTFE-coated glass fibre, which has an estimated minimum lifetime of 25 years. In 2005 the millennium dome was renamed the O2 (after the mobile phone company) and converted into a multifunctional sports and entertainment complex. The complex now houses a number of buildings and is used for many different sporting and cultural events. It will be used during the 2012 Olympics as the venue for gymnastics, basketball and handball finals. The structure is expected to last until 2018, after which developers will be permitted to demolish the Dome and redevelop the site.