I read that Russia is a country of many rivers (hence its name) and I wanted to depict a small bridge over a narrow river...but have no idea how Russians made their bridges nor seen any examples. I thought of making one too small for anything bigger than a truck to get across it.

Write 'Russian bridges' on -> Google. -> Pictures. -> Many pictures of various sizes and models

Problem: finding a picture you can be sure existed in a certain era.

This may not be of much help but the design and construction of both stone arch and wooden bent bridges have not changed much since Roman times.

Michael is right simple stone or wooden bridge will be good.