Thousands of athletes gather every four years to compete in this international extravaganza that alternates between the Summer Games and the Winter Games. The modern Olympics began just before the 20th century and are a revival of games that originated in Greece. The games include numerous symbols and rituals — notably the torch, the flag and the opening and closing ceremonies. There has been some controversy in recent years over the environmental impact of the Olympics, but the spectacle and athleticism of the Games make it an internationally uniting event. (Photo: Flickr)