Roma I was one of the Known Worlds where the Roman Empire lasted into the 20th century, controlling all of Earth.
After Marcus Americanius Scriptor obtained a time ring that allowed him to travel to the other Known Worlds, he named his Earth "Roma I" for convenience. When it was discovered that it was also the most advanced of the Earths where Rome ruled, it became the most influential member of the Empire of Empires. (PROSE: Warlords of Utopia)