Carcassonne, France, showing the classic features of the curtain walls, defensive ditch with arched bridge, and cylindrical flanking towers, with a gatehouse and additional wooden defensive structures, here defending a walled city.
<a href="//commons.wikimedia.org/wiki/User:Pinpin" title="User:Pinpin">Pinpin</a>
CC BY 2.5
<span class="int-own-work" lang="en">Own work</span>