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alternatehistory.com
"Real" World
When the James Blish novelisation of this episode was published there was an extra coda. Holmes has a flash of inspiration and pulls up the appropriate period of TELLURIAN history from the files downloaded from the Tellurian Navy headquarters and there it is.
During the early 300s of Tellus' version of the Roman Empire there were lots of bright lights in the sky above Rome and over half its population disappeared! It was this that triggered the civil war which resulted in Constantinius becoming Emperor.