King Zhaoxiang of Qin
Because King Zhaoxiang had not yet legally come of age (traditionally at the age of 20), his mother, who was now known as Queen Dowager Xuan, became the regent. She was supported by her brothers, Wei Ran and Mi Rong (羋戎), as well as two other sons, Prince Yi (公子悝) and Prince Fu (公子巿), the four of them collectively known as the "Four Nobles" (四貴).
History of the Great Wall of China
Qin was originally a state on the western fringe of the Chinese political sphere, but it grew into a formidable power in the later parts of the Warring States period when it aggressively expanded in all directions. In the north, the state of Wei and the Yiqu built walls to protect themselves from Qin aggression, but were still unable to stop Qin from eating into their territories. The Qin reformist Shang Yang forced the Wei out of their walled area west of the Yellow River in 340 , and King Huiwen of Qin (r.338–311) took 25 Yiqu forts in a northern offensive. When King Huiwen died, his widow the Queen Dowager Xuan acted as regent because the succeeding sons were deemed too young to govern. During the reign of King Zhaoxiang (r.306–251), the queen dowager apparently entered illicit relations with the Yiqu king and gave birth to two of his sons, but later tricked and killed the Yiqu king. Following that coup, the Qin army marched into Yiqu territory at the queen dowager's orders; the Qin annihilated the Yiqu remnants and thus came to possess the Ordos region. At this point the Qin built a wall around their new territories to defend against the true nomads even further north, incorporating the Wei walls. As a result, an estimated total of of Qin walls (including spurts) extended from southern Gansu to the bank of the Yellow River in the Jungar Banner, close to the border with Zhao at the time.