If you don't know, you can find a vault-tec logo on a door in DOOMs prologue. You can also find a dead body in hell wearing an iron helmet from Skyrim, but what if..... It meant something more
In fallout 4 you can find Nirnroot grown on the Prydwen, this plant is native to various regions in the elder scrolls series. What if fallout took place thousands of years after the elder scrolls and the Great War started after the UAC set up shop on Mars. What if Vault-Tec was partnered with the UAC?The iron helmet could be from a Nord warrior banished to hell? I dunno I think I'm going crazy
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Not only is TES set on another planet, Nirn, it has two moons and completely different continents. Fallout takes place on Earth, so the two are not in the same universe. These are simply Easter eggs Bethesda wanted to include in their games.