The troll raid event can't happen until you kill a troll. That means that you know how to kill a troll with the gear you had (or worse gear). You should keep a portal by the stones so that you can quickly change forsaken powers. This would have allowed you to get back to the base that was under attack or to a different one where you could at least eat before portalling to the base that was under attack.

Earth walls and dry moats are what the actual Vikings used for defense. Those things work in game too for every thing except flying creatures.

Edit: You had the wiki open and didn't read about troll raids?