Road bicycle racing is the cycle sport discipline of road cycling, held primarily on paved roads. Road racing is the most popular professional form of bicycle racing, in terms of numbers of competitors, events and spectators. The two most common competition formats are mass start events, where riders start simultaneously (though sometimes with a handicap) and race to a set finish point; and time trials, where individual riders or teams race a course alone against the clock. Stage races or "tours" take multiple days, and consist of several mass-start or time-trial stages ridden consecutively. Professional racing originated in Western Europe, centred in France, Spain, Italy and the Low Countries. Since the mid-1980s, the sport has diversified, with races held at the professional, semi-professional and amateur levels, worldwide. The sport is governed by the Union Cycliste Internationale (UCI). As well as the UCI's annual World Championships for men and women, the biggest event is the Tour de France, a three-week race that can attract over 500,000 roadside supporters a day. History Road racing in its modern form originated in the late 19th century. It began as an organized sport in 1868. The sport was popular in the western European countries of France, Spain, Belgium, and Italy, and some of those earliest road bicycle races remain among the sport's biggest events. These early races include Liège–Bastogne–Liège (established 1892), Paris–Roubaix (1896), the Tour de France (1903), the Milan–San Remo and Giro di Lombardia (1905), the Giro d'Italia (1909), the Volta a Catalunya (1911), and the Tour of Flanders (1913). They provided a template for other races around the world. Cycling has been part of the Summer Olympic Games since the modern sequence started in Athens in 1896. Historically, the most competitive and devoted countries since the beginning of 20th century were Belgium, France and Italy, then road cycling spread in Colombia, Denmark, Germany, Luxembourg, the Netherlands, Portugal, Spain and Switzerland after World War II. However, as the sport grows in popularity through globalization, countries such as Kazakhstan, Australia, Russia, Slovakia, South Africa, Ecuador, New Zealand, Norway, the United Kingdom, Ireland, Poland and the United States continue to produce world-class cyclists. The first women’s road championships were held in France in 1951. A women’s road race discipline was added to the UCI Road World Championships at the 31st edition of the World Championships in 1958 in Reims. Road race types Single-day Professional single-day race