Answer:
Face with a tree, skin like the sea. A great beast I am. Yet vermin frightens me.
If a man carried my burden, he would break his back. I am not rich, but leave silver in my track.
What stays on the ground but never gets dirty?
The eight of us move forth and back. To protect our king from the foes attack.
Forward Iβm heavy, but backwards Iβm not.
If itβs information you seek, come and see me. If itβs pairs of letters you need, I have consecutively three. What am I?