A team of about 10 "flame attendants" is responsible for the 24-hour safe passage of the flame, which is ignited by the sun's rays at the ancient site of Olympia in Greece. Each night three guards guard the torch in a hotel room. "Security people try their best to keep the flame safe. The flame is always burning, whether on the plane or during the relay or overnight. It's kept in the hotel where the core operation team is staying," says a Beijing Organizing Committee spokesperson. The convoy accompanying the torch includes over 20 vehicles provided by the relay city.
Most of this journey is on foot, but other modes of transport have been included over the years. Such as the dog sled, horse, canoe and camel.
In London, it was be carried on two boats, a bike, a bus and the Docklands Light Railway.
For air travel, where open flames are not allowed, the flame burns in the enclosed lanterns.
The torch, the lanterns and the team of attendants, plus other security, fly in a specially-chartered Air China plane bearing an Olympic flame design.
For a trip across the Great Barrier Reef before the 2000 Olympic Games, a special torch was designed to burn underwater.
The flame made its first trip in a plane in 1952 and has also travelled on Concorde.
The torch can counter wind speeds of upto 65 kilometres per hour and stays alight in 50 mm of rain an hour.
In ancient times, the flame burned throughout the Games on the altar of the Goddess Hestia, situated in the Prytaneum, the building used for the post-Games banquets.
This fire was lit by the sun's rays and it was used to light other fires of the sanctuary, such as the altars of Zeus - the Games were held in his and Queen Hera's honour.
The present Olympic torch relay begins at the Temple of Hera several months before the Games, where it is lit by a woman in ceremonial robes using a mirror and the sun.
The Olympic flame was reintroduced to the modern Olympics in Amsterdam in 1928 and the first torch relay was held eight years later in Berlin. It symbolises the Olympic ideal of harmony between nations.