Carteneau Flats
“Reduced to a desolate wasteland by the Calamity, the Carteneau Flats are devoid of all value save for the Allagan ruins scattered across its desolate landscape. With each nation coveting the untold secrets they possess, tensions mounted, threatening to undermine the very foundation of the Eorzean Alliance. To prevent needless bloodshed, while permitting the pursuit of individual interests, the three nations have agreed to a civilized conflict within the borders of Carteneau. To that end, the Grand Companies now call upon regiments of adventurers to help lay claim to this contested domain.
— In-game description
Carteneau Flats is a Region in Eorzea. It holds the large-scale PvP battleground The Borderland Ruins (Secure), the first mode released for Frontline. It is also the setting of the solo duty 
Death Unto Dawn.