The Summer Olympics are the world's largest multi-sport event, and are organized by the International Olympic Committee (IOC) every four years. Selection of the host city is done at an IOC Session four to seven years prior to the tournament, in which the IOC members vote between candidate cities which have submitted bids. As of the selection of the 2016 Olympics, 28 games have been held in 22 cities in 19 countries. Bids have been made by 64 cities in 34 countries. The bid process consists of two rounds. First, cities and national Olympic committees (NOCs) may show their interest and submit a preliminary bid, becoming applicant cities. Through analysis of the questionnaires, the IOC gave a weighted-average score to each city based on the scores obtained in each of the questionnaire's eleven themes: political and social support, general infrastructure, sports venues, Olympic Village, environment, accommodation, transport, security, past experience, finance, and legacy. IOC's executive committee then selects a short-list of candidate cities. The candidate cities are investigated by the IOC Evaluation Committee, who make an evaluation report. These submit a more extensive bid book and are subject to additional evaluation, which is presented to the IOC members. Voting occurs as an exhaustive ballot, which may occur through multiple rounds until a single city holds a majority of the votes. IOC members from a candidate NOC may not vote in any round while their country remains in the election. The first three games were not subject to bids; the first IOC Session, in 1894, awarded the first games to Athens (1896) and Paris (1900), respectively. The 1904 Olympics were initially awarded to Chicago, but then moved to St. Louis to be co-located with the World Fair. A system with bids was introduced ahead of the 1908 Olympics, and were awarded to Rome. After the 1906 eruption of Mount Vesuvius, Italy returned the games to IOC, which awarded them to London. The 1916 Olympics were awarded to Berlin, but canceled due to the First World War. The 1940 Olympics were originally awarded to Tokyo, but after the 1938 break-out of the Second Sino-Japanese War, they were returned to the IOC, who awarded them to Helsinki. The games, and the 1944 Olympics awarded to London, were ultimately canceled due to the Second World War. The 1956 Olympics were awarded to Melbourne, but Australian horse quarantine rules forced the equestrian events to be