This year's official mascots are named after Greek Gods; Phevos, the god of light and Athena the goddess of wisdom and patron of the city of Athens.
The original marathon
The marathon was first run in 1896. It celebrates the legendary feat of a Greek soldier who, in 490 BC, is supposed to have run about 25 miles from Marathon to Athens with the news that the Persians had been defeated, before keeling over and dying.
In 1924, the Olympic marathon distance became 42,195 metres (26 miles 385 yards). This is based on the distance between Windsor Castle and the royal box in the London stadium; the route of the marathon during the 1908 Olympics.
Before the 1970s, only amateurs officially took part in the Games but since that time professional athletes have joined in.
The Paralympics Games, for athletes with disabilities, were first held in Rome in 1960.
The first separate winter Olympic Games were held in Chamonix-Mont Blanc, France in 1924.