Which han dynasty reform was reintroduced during the tang dynasty?

The Tang dynasty (Chinese: 唐朝[a]) was an imperial dynasty of China preceded by the Sui dynasty and followed by the Five Dynasties and Ten Kingdoms period. It is generally regarded as a high point in Chinese civilization, and a golden age of cosmopolitan culture.[4] Its territory, acquired through the military campaigns of its early rulers, rivaled that of the Han dynasty, and the Tang capital at Chang'an (present-day Xi'an) was the most populous city in the world.