A century ago London hosted the Fourth Olympiad in 1908 Summer Olympics. It was first time London hosted Olympic Games, there were 24 sports and approximately 2,000 athletes participated, representing 22 countries.

The 1948 Summer Olympics, officially known as the Games of the XIV Olympiad which was held in London, a record 59 nations were represented by 4,104 athletes. Upcoming 2012 London Olympics will be held in London. It will become the first city to stage the Olympics three times. Games of the XXX Olympiad are the official name of Summer Olympics 2012. There are 26 sports and approximately 11,000 athletes participated, representing 204 countries.

The opening ceremony

• 15,000 square metres of staging - equivalent to 12 Olympic-sized swimming pools. A flying system that can lift 25 tonnes - that is the same as five elephants.
• There will be 12,956 props, which is more than 100 times more than used in a West End musical.
• A million-watt PA system using more than 500 speakers and 50 tonnes of associated sound gear - which is double the amount of speakers than on the main stage at Glastonbury.
• The design team have made enough scale model pieces to cover a 100 metre running track. Every performer has been represented by a plastic figurine.
• Across all four opening and closing ceremonies at the London 2012 Olympic and Paralympics there will be:
• 25 containers full of scenery and props and 75 containers of costumes full of 23,000 costumes. Some cast members will wear more than one costume.
• A cast of 15,000 volunteers will work across all four ceremonies. People aged from 18 to 90 years old have auditioned. They have come from across the UK and include people who watched the 1948 Games live, according to London 2012.
• A total of 12 hours of music working with an orchestra of around 60 musicians is part of the programme. Up to three months of recording time in the studio and 36 hours in dedicated drum tuition will be needed to get ready for the big events, organisers estimated.
• Four billion people across the world are expected to watch the opening ceremony
• Businessman Sir Martin Sorrell, the founder of WPP, the world's largest advertising agency, has predicted that the equivalent airtime value of the four ceremonies will be worth between approximately £2 billion and £5 billion.