Greatest shows on earth: How expos changed the world

World expos have created some of the world's most famous monuments, not least the Eiffel Tower, the centrepiece of the 1889 Paris expo. Photo: AFP

International expos, or world fairs, draw millions of visitors to a chosen city every few years.

Over two centuries, these mega events have introduced the world to tomato ketchup, colour television and mobile phones and have left us the Eiffel Tower, Seattle's Space Needle and Shanghai's enormous China Pavilion.