The winner of the Indianapolis 500 celebrates by drinking milk

The Indianapolis 500, first run in 1911, is one of the oldest and best-attended single-day sporting events on Earth. Drivers complete 200 laps of the 2.5-mile oval - exactly 500 miles (800 km) - racing counter-clockwise before crowds of several hundred thousand.

Its strangest tradition is the finish. In 1936, three-time winner Louis Meyer asked for a glass of buttermilk in Victory Lane, a drink his mother swore cooled him on hot days. A photographer caught him swigging it, the image ran nationwide, and an alert dairy-industry executive recognized free advertising when he saw it. The milk has been handed to the winner deliberately ever since - a sponsored ritual the dairy board has guarded for nearly 90 years.

It isn’t always welcome. In 1993, Brazilian Emerson Fittipaldi pointedly sipped orange juice instead, partly because he owned Florida orange groves. The snub drew boos and a wave of fan backlash, and the milk has gone unchallenged since.

A bottle of milk, swigged on camera, has been the prize ritual for nearly a century.

Modern racing leaves nothing to chance. Each driver in the field submits a milk preference in advance - whole, 2%, or skim - and that published list is read out so the right bottle is chilled and waiting at the bricks.

The very first race, in 1911, was won by Ray Harroun at about 74.6 mph. He drove solo while rivals carried a riding mechanic to watch the track behind, and is credited with fitting one of the first rear-view mirrors to a racing car to do without one.