tang cities, which were protected by defensive walls and gates, also were based on the cardinal points of the compass. The Tang imperial city of Changan (modern-day xian) had major east-west and north-south thorougfares that defined the subdivisions of the city. The imperial palace compound was in the north ; beyond the palace and outside the northern city walls was an imperial park that included a large artificial lake, which served as a royal hunting preserve and private space for the emperor and his court.