Lest Darkness Fall by L. Sprague de Camp

is a pre-WWII time travel novel where the protagonist Martin Padway (coincidentally an archeologist & historian) gets hit by lighting while visiting Rome's Parthenon and is flung back to 535 A.D. where he has the chance to staunch the advance of the Dark Ages by keeping the light of civilization shining a bit longer.

He does this by introducing such things as stirrups, the printing press and gunpowder. His knowledge of the era's politics and historical figures stands his in good stead as he battles Belisarius, who is trying to retake Italy for Justinian's Eastern Empire while the various factions in Rome squabble over various theological issues of the day.

Lest Darkness Fall is one of my favorite novels of all time, so when Q used the phrase in the Q4532 drop, I immediately thought of the novel. I may just re-read it again.