To protect the North, the founding emperor of the Ming Dynasty, Zhu Yuanzhang, sent one of his most capable sons, Zhu Di, to the area around the old Khanbaliq to guard the north. He rebuilt the defenses, adding bricks and towers to the system of pretty good, if not great, earthen walls which marked the northern boundary of China.
While history does not record whether or not he was able to get the Mongolians to pay for the wall, Zhu Di fought the Mongolians on their own turf on more than one occasion and kept the empire safe. But when his father died, Zhu Di was passed over in favor of one of Zhu Yuanzhang’s grandsons.