The flat and fertile plains of the Trident provided the people of the Riverlands with abundant food and resources. Yet this geographical feature made the region exceptionally vulnerable to a sweeping invasion by a large army, especially since river travel allowed vessels to easily drift downstream.
Indeed, during several major wars in history, the Riverlands—sandwiched between the Westeros, The North, the Vale, and King's Landing—had invariably been the first territory trampled flat by the various armies.
Within the entire River Plains, Riverrun stood as the sole fortress that was easy to defend and difficult to attack, usually ending up as the solitary castle left standing in the end.
Chapter 24