Tongwan City, also conventionally called Baichengzi, was the capital of Balkh Empire founded by leader of Hun in East Jin Dynasty. Tongwan City site comprises of outer city and inner city. Inner city again is divided into two parts, east city and west city. From east to west orderly lies the outer city, east city and west city. The outer city is rectangle in plane, with a perimeter of 4700 meters. The east city and west city was separated by a wall. The perimeter of east city is 2566 meters and that of west city is 2470 meters. There are four coigns higher than the city walls on four angles of east city and west city, taking on a shape of square or rectangle in plane. The coign in the southwest angle is as high as 40 meters. The existing wall is from 1 to 10 meters higher than the ground.
Tongwan City is the only comparatively well preserved early state capital site of northern minor groups today. Its majesty palace standing on sands, white walls as hard as stone, serried horse pens, towering turrets, and the unique structure of secret room in ghost house all clearly sketches out the profile and scale of the Balkh Empire capital, with a name meaning “unifying the world and governing all places” Tongwan City makes itself a archeological and traveling destination to explore and study the architectural art of nomad as well as the culture and history of the period from Balkh to West Balkh, which lasts 5 century by its unique architecture and various precious antiques.