There was a mountainous region towards the rear of the Bitter Water Prefecture, and there were two trails in the mountain roads which led directly to the Loulan Duchy. However, these two roads were far too small. Some parts were just a single narrow valley road. War horses were able to force their ways through, but carriages carrying materials and supplies would not be able to cross it.
Such terrain was not favorable for the deployment of troops. In the past, Lex had used them to send people to fortify wide open areas. There were four castles, so only an extremely limited number of troops were able to live in them. However, if those two roads were opened fully, assuming that bridges were built and the valley was cleared using explosives, then the duration of travel from the Bitter Water Prefecture to Loulan Duchy would be decreased from more than one month to half a month.
