오슈 후지와라 씨
The area of present-day Hiraizumi was part of ancient Mutsu Province. It was the home of the Northern Fujiwara clan for about 100 years in the late Heian era, during which time it served as the "de facto" capital of Ōshū, an area containing nearly a third of the Japanese land area. At its height the population of Hiraizumi reached 50,000 or more than 100,000, rivaling Kyoto in size and splendor.