I was exploring the front gate of Markarth tonight and i found that there are two not so hidden but no so eaisly found access point that get you to the upper battlements on the main gate outside the city, along with thoes there are also many arrow slits on the gate walls, and over ther main gate its self there is a grate which looks like it would be used to pour hot oil on would be attackers or some type of magical trap could be set there. Markarth and Riften both have watch towers leading up to the citys main gates, neither of them had big battles take palce there in the civil war quest line. I am proposing that both citites will fall under siege in a new DLC im putting my money on Markarth though because of the defenses the city walls have. I can not say what exacatly will happen maybe the foresworn will attack Markarth and maybe the thalmor will try and take over riften, who knows just atheory based on my observation.
Thoughts?