Some cities are just places where a lot of people live and work. Some are seats of worldly authorities, elevating them above others. And then there is the Holy City, a site so intrinsically tied to a particular religion that it became a symbol of faith all by itself. In peacetime, it will result in thousands to millions of devoted pilgrims visiting it every day. In wartime, expect it to be defended to the last breath, even more so than a national capital (unless it is the national capital), and the consequences if it is ever sacked by an invader are a lot graver. Compare Capital City.