As the eastern capital of the Sui and Tang empires (589-907), Luoyang saw its heyday, during which time it enjoyed a prosperous economy and flourishing culture. The eastern capital was established at a location of strategic importance with the Yellow River in the north, the Yique Valley in the south, the Hulao Pass in the east and the Hangu Pass in the west. With a population exceeding one million, it was another political, military, economic and cultural center of the Sui and Tang dynasties, in addition to Chang'an, the official capital. Peripheral areas that include present-day Gongyi, Yanshi, Mengzhou, Mengjin, Xin'an, Yiyang, Yichuan, Ruzhou and Dengfeng in Henan province acted as protective environs for the eastern capital.