Lest Darkness Fall Author:L. Sprague De Camp The Roman Empire had spread order, knowledge, and civilization throughout the ancient world. When Rome fell, the light of reason flickered out across the Empire. The Dark Ages had begun; they would last a thousand years. Could a man from the 20th century prevent the fall of Rome? When lightning struck and he was hurled backward into the sixth ce... more »ntury, the question became anything but academic to Martin Padway, but even forearmed with a knowledge of 20th century technology and of events to come, what could one man do? But Padway must try, lest darkness fall...« less
Not at great example of this sub-genre, but it is entertaining and more realistic. I checked on Fantastic Fiction and this novel is one of the first three books he wrote, in 1941.