What is the importance of Trelburg in the novel, Eaters of the Dead: The Manuscript of Ibn Fadlan?

Trelburg is a military camp the warrior party stops at during their journey North. There are few women or children living in this fortress city. The encampment is located on a point of land created by the joining of two rivers. The town is encircled by a wall. A second wall inside the first protects the town itself. The long houses are arranged in groups of four to make a total of sixteen houses. Each house has only one entrance/exit and each entrance faces a different direction. The doors of the houses are very low so that one man can remain inside and cut off the heads of intruders.