If you're trying to worm your way through traffic on Sunday or in the crowds at the Mall to cheer on a relative, it will be hard to picture any other race matching the sheer size and scale of the London Marathon.
Yet the scuttle through the Big Smoke is just one of the world's six Marathon Majors alongside Chicago, Boston, Tokyo, New York and Berlin.
The pavements of each of those world cities take a similar pounding each year as hundreds of thousands of amateur athletes test themselves over 42 km, with elite runners also competing against each other over a year-long scoring system of the races as part of the World Marathon Majors championship.
This year's London Marathon marks the second event of the current series which will wrap up at the 2017 Boston Marathon on 17 April. Runners are scored based on their best two race finishes and the eventual winner can take home a prize of $500,000.
Winners of individual marathons also receive a healthy reward - but the amount differs from race to race. While the distance may stay the same between the six races, they differ on every other measure:
1. Applications - Tokyo
2. Participants - London
3. Finishers (2015) - New York
4. Spectators - Chicago
5. Prize money - Boston
6. Economic impact - New York