The fortress was built from AD 475 to 538. However, it remained a fortress throughout the Baekje, Goryeo, and Joseon dynasties. As such, it underwent repairs and continued to be fortified throughout its history. Some parts of the fortress are original, but different sections date to different time periods over about a 1,000 year span. Its wall is 2,660 m in length, with a couple of steep sections (nothing too high though). I found it fairly easy to walk along.
The fortress was originally built to protect the royal palace. Aside from the Royal Palace Site, around they have discovered 80 structures including roads, reservoirs, ponds, warehouses, and drainage channels.