The Abka Line is a string of fortifications dividing the Western Plains Province from the Abka State in the Earth Kingdom. Its Northern terminus extends past the modern borders of these provinces and into the Shanbei province; in the south it reaches the mountains in Hubei. The line was intended to prevent mass movement of mounted nomads into the central plains of the Earth Kingdom, where they could threaten the core provinces. A secondary part of the Abka line separated Liuchu from the Western Plains Province, though it was not completed before the line as a whole fell out of use.
The Abka line became unnecessary in the 780s BG with the Yonggan ascendancy under the Great Ri; the Yonggan were able to maintain good relations with the Western Nomads when their conquest dynasty took control in Ba Sing Se. After the fall of the Ri in 620 BG, the nascent Hao Ting partially repaired the line, which had been allowed to fall into disrepair, and garrisoned it. However, the Abka mostly changed allegiances peacefully and never mounted a coordinated assault on the Central Earth Kingdom during the dynastic transition. By the mid-500s the line was abandoned again, and except for a few forts, it is now entirely abandoned and mostly in ruins.