I found the text with the coma and I didn't check the original. Even though, I think there can be different versions, with coma or without, because both make sense, and this would not be the first case in history, since copists have made mistakes in their jobs. But you are right, they have different meanigs: with coma I would find it means "indeed" (as I translated into Spanish,"es decir"
.I would appriciate if you gave me your point of view. Without coma, "quod" takes part in the relative clause, and we should translate, as you said: "which is the fortified town..."
I also made a terrible mistake by not translating the final clause "ut pro castris conlocaverit". I will correct this.
I understood there were three principal verbs in the sentence and I translated them. To me, there is a principal clause with its three verbs (reduxit, coepit and iussit)and two other subordinate clauses: ut pro castris conlocaverat and the absolute ablative at the begining.
You are also right abiut the meaning of "impedimenta" I should have checked the dictionary first, but it sounded too clear to me! I'll be more careful next time!
Well, these are my points of view anyway!
Thanks for your comments!