Introduce radio to the Romans. They had the metallurgy to create coils. Even a simple Morse code system would easily keep their empire going. Probably end up like that Star Trek TOS where Centurions are carrying sub-machine guns, though. If want to read what a great SF writer did with this (guy from 1938 ends up in 535AD), read “Lest Darkness Fall”
Introduce radio to the Romans. They had the metallurgy to create coils. Even a simple Morse code system would easily keep their empire going. Probably end up like that Star Trek TOS where Centurions are carrying sub-machine guns, though. If want to read what a great SF writer did with this (guy from 1938 ends up in 535AD), read “Lest Darkness Fall”