With the exception of the Naktong delta to the south, and the valley between Taegu and P'ohang-dong, the terrain is extremely rough and mountainous. Northeast of P'ohang-dong along the South Korean line the terrain was especially treacherous, and movement in the region was extremely difficult. Thus, the UN established the Pusan Perimeter in a location outlined by the Sea of Japan to the south and east, the Naktong River to the west, and extremely mountainous terrain to the north, using the terrain as a natural defense. However the rough terrain also made communication difficult, particularly for the ROK forces in the P'ohang-dong area.