The term "track and field" is intertwined with the stadiums that first hosted such competitions. The two basic features of a track and field stadium are the outer oval-shaped running track and an area of turf within this track—the field. In earlier competitions, track lengths varied: the Panathinaiko Stadium measured 333.33 metres at the 1896 Summer Olympics, while at the 1904 Olympics the distance was a third of a mile (536.45 m) at Francis Field. As the sport developed, the IAAF standardised the length to 400 m and stated that the tracks must be split into six to eight running lanes. Precise widths for the lanes were established, as were regulations regarding the curvature of the track. Tracks made of flattened cinders were popular in the early 20th century but synthetic tracks became standard in the late 1960s. 3M's Tartan track (an all-weather running track of polyurethane) gained popularity after its use at the 1968 US Olympic Trials and the 1968 Summer Olympics and it began the process in which synthetic tracks became the standard for the sport. Many track and field stadiums are multi-purpose stadiums, with the running track surrounding a field built for other sports, such as the various types of football.