Mutsu was one of the 68 ancient provinces of Japan, the largest of them all, occupying what is now Fukushima, Miyagi, Iwate, and Aomori prefectures, and a small portion of what is now Akita prefecture. Located in northeastern Honshu and covering much of the region now known as Tohoku, Mutsu was bordered on the east by the Pacific Ocean and on the north by the Tsugaru Strait. To the west were Dewa and Echigo provinces, and to the south were Kozuke, Shimotsuke, and Hitachi.
In very ancient times, the land that would later become Mutsu province was occupied by the Emishi - a non-Japanese "barbarian" race of horse-riding hunter-gatherers. Over the course of the Nara and Heian periods, the Yamato state gradually conquered the Emishi, pushing them northward and gradually extending the province of Mutsu as they went.
In the 12th century, southern Mutsu was the location of the Northern Fujiwara capital at Hiraizumi - the center of a quasi-independent state that lasted nearly a century and rivaled the imperial capital of Kyoto in terms of wealth and power.
During the Sengoku Period, the mighty Date clan ruled most of Mutsu province from their castle town of Sendai, the most famous Date daimyo being Date Masamune.
Today, the term Mutsu is rarely, if ever, used. However, the prefectures that make up what used to be Mutsu are still affectionately known by the nickname Michinoku, meaning something like "the end of the road" - a pun on the two Chinese characters used to spell "Mutsu."