Reminds me of Lest Darkness Fall[1], a 1939 novel about an archeology professor who is transported back in time to Rome under the Ostrogoths on the eve of Belisarius' invasion to reconquer Italy for the Eastern Roman Empire under Justinian.

The hero of the novel, Martin Padway, gets his start teaching Arabic numerals to a Syrian banker in Rome, and then distilling brandy. By the end of the novel he's running a newspaper and has a semaphore telegraph network set up throughout Italy. Good fun reading.

[1] https://en.wikipedia.org/wiki/Lest_Darkness_Fall