The London Eye is a giant Ferris wheel situated on the banks of the River Thames, in London, England. The entire structure is 135 metres tall and the wheel has a diameter of 120 metres. It is the tallest Ferris wheel in Europe, and the most popular paid tourist attraction in the United Kingdom, visited by over 3.5 million people annually. When erected in 1999, it was the tallest Ferris wheel in the world, until surpassed first by the 160 metres Star of Nanchang in 2006, and then the 165 metres Singapore Flyer in 2008. The wheel's 32 sealed and air-conditioned ovoidal passenger capsules are attached to the external circumference of the wheel and rotated by electric motors. Each capsule represents one of the London Boroughs, weighs 10 tonnes and holds 25 people, who are free to walk around inside the capsule. The wheel rotates at 26 cm per second (about 0.9 km/h) so that one revolution takes about 30 minutes. It does not usually stop to take on passengers; the rotation rate is slow enough to allow passengers to walk on and off the moving capsules at ground level.