Here’s a list of the seven biggest marathons in the world. The United States and Japan host the lion’s share of the largest marathons around the world. Hosting tens of thousands of runners requires a big city and the marathons on this list are in some of the most prestigious cities in the world. I ranked marathons by number of finishers. The numbers were pulled from 2015 press releases and posted race results. The largest marathon is almost two times bigger than marathons six and seven.