Answer:
I am a protector. I sit on a bridge. One person can see right through me while others wonder what I hide.
What goes through cities and fields but never moves?
Dead on the field lie ten soldiers in white killed by one blade yet there was no fight. What are they?
I tremble at each breath of air, and yet can heaviest burdens bear. What am I?
I am all around, yet to me you are half blind. Sunlight makes me invisible and difficult to find. What am I?
It flows out of the soil, It burns you if it boils, And holds us in its coils, More valuable than gold, As black as it is old.