Being aware of the way the Tang dynasty designated Chang'an in the west as the capital and Luoyang in the east as the second capital, Heian-kyo referred to the area to the west of Suzaku-oji Avenue as Choan (Chang'an) or Ukyo and the one to the east as Rakuyo (Luoyang) or Sakyo.
平安京では、唐が西の長安を首都、東の洛陽を副都としたのを意識し、朱雀大路の西を長安（右京）、東（左京）を洛陽と称した。