On 20 August 1920, the owners of four local Ohio football leagues convened to form the American Professional Football Conference. Football star of the day Jim Thorpe was brought on as president in an effort to legitimize the nascent league. The members were banking on the growing popularity of the game, but they could scarcely have imagined how successful the National Football League would become. To commemorate this historic day, we looked through the Sotheby's archives at some of the rare football memorabilia that have passed through our days.