The Taixue ("National University"), was the highest educational institution in imperial China. During the reign of Emperor Wu of Han (r. 141-87 BC), Confucianism was adopted as the state doctrine. The Confucian scholar Dong Zhongshu suggested establishing a National University ("Taixue") in the capital, Chang'an, so that erudites could teach the Classics. Teaching at the Taixue was a prestigious job because the emperor commonly picked from among them for appointment in high offices. At first the Taixue had only 50 students but increased to around 3,000 by the end of the millennium. Under the reign of Wang Mang (r. 9–23), two other educational institutions called the Biyong and Mingtang were established south of the city walls, each able to house 10,000 students. The professors and students were able to exercise some political power by criticizing their opponents such as governors and eunuchs. This eventually led to the arrest of more than 1,000 professors and students by the eunuchs.