A number of weapons and plot devices seem to borrow from ideas seen in the Marathon series of first-person shooters made by Bungie in the early to mid-1990s
These include the concept of MJOLNIR "cyborgs", the supersoldier main character, the weapons, artificial intelligences, and even some of the alien creatures. Upon close inspection, crew members of the Pillar of the Autumn have the Marathon symbol on their uniforms, and the symbol is even embedded in the Halo logo itself. The Elites from Halo are somewhat similar (in their appearance, not their role) to Marathon's Pfhor. Hunters appear in both games filling the same roles. The Hunters from Halo, though much larger, also clearly share design elements with the Hunters from Marathon. A type of alien that was modeled for Halo 2 but later cut is nearly identical to the Drinniol from Marathon. Also, both games use uniform color to differentiate between different ranks of aliens (and crew members), with higher ranks being stronger and harder to kill. There are two multiplayer gaming options, a version of king of the hill and a game called Oddball (called "Kill the Man with the Ball" in Marathon), which are present in Marathon's multiplayer mode.
These large similarities led to early speculation that Halo took place in the same universe as Marathon, only with different time frames; however, this was later proved highly unlikely. According to both the Halo video games and books, the events in Halo coincide with the events in Marathon. However, due to technology differences (the lack of transporter technology in Halo, for one), this is impossible. On Bungie's own Marathon page, there is a Q&A which states, "Is Marathon the prequel to Halo? [...] No, Marathon is a separate story, with wholly different characters, story and gameplay."