Mogami clan
The first castle on this site dates to the middle of the Muromachi period, when Shiba Kaneyori established himself as lord of the surrounding area of Dewa Province and built a fortified residence on the site of what is now the inner bailey of Yamagata Castle. The Shiba clan was a strong supporter of the Ashikaga shogunate and the Northern Court. Shiba Kaneyori later changed his surname to "Mogami", and the Mogami clan continued to rule for about 275 years. However, by the Sengoku period, the Mogami had lost much of heir power due to a succession of internal conflicts and short-lived leaders. The aggressive Date clan invaded Mogami territory and after a series of battles, reduced the Mogami to a subordinate position. However, the Date clan itself then fell victim to internal political conflicts. Taking advantage of the situation, Mogami Yoshimori regained his independence, and married his daughter to Date Terumune. Their son was Date Masamune, and this relationship provided security for the Mogami clan.