Alma 22

And now it came to pass that Moroni did not stop making preparations for war or to defend his people against the Lamanites; for he caused that his armies should commence, in the commencement of the twentieth year of the reign of the judges, that they should commence in digging up heaps of earth round about all the cities throughout all the land which was possessed by the Nephites. And upon the top of those ridges of earth, he caused that there should be timbers, yea, works of timbers, built up to the heighth of a man, round about the cities.