What was restored and streghtened inder the ming emperor to help protect against invaders?

Under the Ming emperor, the Great Wall of China was restored and strengthened to protect against invasions, particularly from northern tribes such as the Mongols. The Ming dynasty invested in extensive fortifications, including watchtowers and garrisons, enhancing the wall's defensive capabilities. This effort not only aimed to secure the empire's borders but also to assert the power and stability of the Ming rule.