Kim, Jinwung (5 November 2012). A History of Korea: From "Land of the Morning Calm" to States in Conflict. Indiana University Press. p. 36. ISBN978-0253000781. Retrieved 15 July 2016. "Because Pyongyang was located in the vast, fertile Taedong River basin and had been the center of advanced culture of Old Chosŏn and Nangnang, this move led Koguryŏ to attain a high level of economic and cultural prosperity."
britannica.com
"Pyongyang". Encyclopædia Britannica Online. Retrieved 19 April 2015.