永定河
Both Yan and Ji were situated along an important north–south trade route along the eastern flank of the Taihang Mountains from the Central Plain to the northern steppes. Ji, located just north of the Yongding River, was a convenient rest stop for trade caravans. Here, the route to the northwest through the mountain passes diverged from the road to the Northeast. Ji also had a steady water supply from the nearby Lotus Pool, which still exists south of the Beijing West railway station. The Liulihe settlement relied on the more seasonal flow of the Liuli River. Some time during the Western Zhou or early Eastern Zhou dynasty, Yan conquered Ji and moved its capital to Ji, which continued to be called Jicheng or the City of Ji until the 2nd century AD. Due to its historical association with the State of Yan, the city of Beijing is also known as Yanjing () or the "Yan Capital."