The City of Arrieta is mentioned to be the closest Demon city containing a red mist obelisk to the human kingdoms. It is also mentioned to be one of the few remaining cities that the Sea Sky-Realm did not destroy or invade.
After the first Battle of Divine Will, the humanity was pushed out of the Land of Dawn, into the Fertile Plains. Here, they established the Witch Federation, also known as the Union. Arrieta was one of the three Holy Cities of the Union.
This Holy City, like the other two, fell to the demons during the second Battle of Divine Will. With its and Starfall City's fall, the Union gradually retreated southward, to the corner of the plains. After the last Holy City, Taquila, also fell, the Union was defeated. The survivors fled to the "Barbarian Lands", a tiny corner of the continent, eventually founding the Four Kingdoms.
Arrieta is located in the Fertile Plains. Like the two other Holy Cities from the Union, it is built upon a God's Stone mine.
To the north lays the Land of Dawn, also occupied by the Demons. In the south of the Fertile Plains are the Four Kingdoms.