I was wondering if anyone might be able to help me recall a book series that I read several years ago. I don't even remember the author but I do remember the general storyline.
The character is walking and runs into a light which turns out to be a portal. He walks into it or in some way or another gets into it and is transported to what initially seems like the distant past. Eventually he runs into some natives and they take him in and teach him the language. Eventually he runs across and piece of glass that says United States Air Force (maybe a different branch, I am not sure) an