- For the city of the same name, see: Marathon (city).
Marathon is a rogue terrestrial planet on the outer edges of the Cyrannus system. Marathon is known for its unusually dense material concentrations within its crust.
During the First Cylon War, the Cylons use Marathon as a strategic site, likely for the material wealth it possesses for war materiel. Additionally, given the planet's rogue nature, FTL travel is precarious making it even more unlikely for Colonials to utilize it.
Utilizing data provided by Praetor Samanta Agathon during the capture of Galactica by Cylon forces, Helena Agathon performs accurate calculations to find Clothos' base at Marathon—located in FTP jump range of Helios Alpha and Helios Beta—thus leading to the inevitable Battle of Marathon and the rescue of Admiral Jubal Sarkis (Battlestar Galactica Deadlock).