An existing yet never implemented zone for Everquest, the Plane of War, much like the city of Veksar and the Kunark expansion, was a zone slated for release with Planes of Power yet scrapped and not included when PoP went live. Reports and rumors at the time stated that the mechanics involved for the intended premise of the zone were unworkable in time for the launch and rather than change the intent and make the Plane of War a more traditional zone without the war mechanics involved it was put aside to be finished later.
The zone can be viewed as it does exist as a finished zone and the files are available if you can view them. The probable entry and graveyard area of the zone are set in a hilly, grassy area with trees leading down to a sparse and desolate open ground in front of the large wall and gates leading to the courtyard of Drunder. The courtyard area is grey and flat, with numerous catapults, low walls, crates and other accoutrements of a battlefield. To the left and right are two large, two story, multi-roomed, similar buildings, supposedly meant to be keeps for Tallon and Vallon Zek as they fought an unending war across the courtyard to train and strengthen their followers and other inhabitants of the plane. On the third wall directly across from the entrance to the courtyard is the wall and large entryway to Drunder, the fortress of zek, which consists of little more than a single large room and a wall across that end of the zone, there is enough room in this area for a fight with a boss enemy or it could simply be the zone area for Drunder.
Rumors, reports and speculation would indicate that the Plane of War was meant to function along the same lines as the Devastation/Sverag zones in the later Prophecy of Ro expansion. Tallon and Vallon Zek were meant to inhabit the two keeps opposing each other in across the courtyard and players were meant to participate in some way with their ongoing war in order to gain access to the fortress of Rallos himself. It was this difficult and at the time innovative mechanic that ended up being the deathnell for the Plane of War, problems with the war mechanic were too difficult to overcome in time for the launch so the Plane of War was scrapped and Tallon and Vallon were moved to Drunder as well, although it's possible they could have appeared in both zones as different events/targets. Much like the city of Veksar in the Ruins of Kunark expansion the Plane of War was listed as one of the zones to be released in the Planes of Power expansion yet was too difficult to complete in time for launch, unlike Veksar however the Plane of War has yet to make its belated appearance in the world of Norrath. Signs of the plane can be found in game, the stone meant to lead to the plane is in the ring with the entrances to the planes of Tactics, Valor, etc. Due to how dated the file looks now, the changes that would have to be made to PoP flagging and the amount of time since a free zone was released to Everquest along the lines of Veksar, Stonebrunt, Jaggedpine, etc, it seems unlikely the Plane of War will ever appear in game.