 Complete the following phrase:  The fortress had a relatively advanced military design, is octagonal in shape with 3-meter thick stone walls, and was surrounded by an earthen wall and a moat. It contained five towers and two gates. Several rows of embrasures faced east, north and west and were designed for various artillery types. Whereas the fortress was hard to conquer when properly defended, its remote location from Turkey meant that its garrison was often understaffed, allowing Russian troops to bypass it in 