The Cross-Time Engineer (Adventures of Conrad Stargard, volume 1) by Leo Frankowski

[james_davis_nicoll]

A Polish engineer is transported into the past, ten years before the first Mongol invasion of Poland. Luckily for him, his allies include the book's author.

The Cross-Time Engineer  (Adventures of Conrad Stargard, volume 1) by Leo Frankowski 

Comments

[(Anonymous)]

The Soviet astronaut in N&P's Lucifer's Hammer had the same idea, I think - Hammerfall had pushed humanity back to feudalism, so his job was to get it back to capitalism.