Shapur II has the record for the longest reign in the history of Persia, 70 years, out of which he ruled personally for 54 years. During the first sixteen years of his life, the power in the country was in the hands of Shapur's mother and her husband Vahram, but in the year 309 C.E. Shapur became the king of the Persian Empire at a very young age. Shapur was probably the greatest military genius Iran had seen since Arashk I, founder of the Parthian empire. Shapur was able to humiliate the Romans in several battles throughout Mesopotamia, and this was all because of his outstanding military tactics. Although the Romans possessed much better armor and military equipment, Shapur was still able to defeat them in battles and keep the Persian army strong-willed and valiant. In a few short years, Shapur defeated all of the minor kingdoms that had dared to declare independence in his absence. He expanded his empire from Punjab in northern India to the north of Caucasus, and from borders of present day China to the edge of Egypt. Shapur also limited the power of the priests and forced them to yield their semi-independence status in favor of the central government's authority. In short, Shapur II started the Golden Era of Sasanian dynasty; an era that lasted for surprisingly long time, with inevitable lapses here and there. This great king brought the Romans down to their knees and took back all the lands that were taken away from Narseh in the 298 peace treaty. .
.
.
II. Constantine.
During his reign, Shapur was constantly confronting Central Asian tribes who had taken advantage of his minority to regain much of their former territory held by Persia. Later, however, Shapur crushed their kingdom in the east and annexed the area as a new province. By doing this, not only did Shapur increase the size of the Persian Empire, but he also acquired the support of the Asian tribes called the Chiniotes, and got them to help him in his campaigns against the Roman armies.