From Tar Valon Library
Darulna is a city in Arad Doman, large for the area of Arad Doman it is in. The city is surrounded by a sturdy granite wall, twenty feet high, that makes it sold, though not beautiful. It is the best fortified city in the region, which is why Rodel Ituralde chose it for his trap against the Seanchan.
Reference: The Gathering Storm, Chapter 12).