Tartaros

Tartaros (冥府の門, タルタロス, Tarutarosu) was one of the three major Dark Guilds and a member of the Balam Alliance, alongside Oración Seis and Grimoire Heart.

History
Despite there not being any factual knowledge of the Guild, such as their base of operations or the count of their members, it is said by few witnesses that they are a group that gathers to worship Demons. According to Warrod Sequen, they may have one of the Books of Zeref in their possession.

Location and Building
The Tartaros guild convenes in a large building located in what appears to be a barren wasteland. Standing among the rocky landscape, the building takes the form of a giant, slight ruined, castle. The structure itself is very big in size, containing at least three separate sections all atop one another. The two main bodies of the castle are noticeably squarer in shape and decorated with numerous crenulations, whilst the turrets and roof of the castle are more curved, their balustrade lined with decorative machicolations and their spires topped with fancy ornaments. At the gate to the castle stand two large statues.

Surrounding the Tartaros headquarters and protruding from the rock are a number of spines, these appearing quite large in size. Whether they are part of the natural landscape or were put there is unknown.

Silver Fullbuster, one of Tartaros' core members, described the entire building as "a sickening piece of architecture".

This castle itself is located on a floating island, shaped like, as well as named, Cube.

Goal
The goal of Tartaros is to use a weapon called Face to wipe out all Magic from the continent. The reason for their intent to take away Magic from the continent is so that they can gather Curse Power in order to revive their Master E.N.D. They would then with their Master return to their creator Zeref. Though most of them are unaware, they wanted to return to Zeref in order to kill him.

Strength
One of their members, the Devil Slayer Silver, was able to freeze the entire Sun Village, its giant occupants, and even the Flame Dragon Atlas Flame, alone. Another member, Jackal, single-handedly killed the entirety of the Magic Council (with the exception of Doranbolt) in a few explosions. According to Cobra, all members of Tartaros are Demons from the Books of Zeref, with the strongest Demon, E.N.D., being their leader.

Trivia

 * Tartarus (/ˈtɑrtərəs/, tar-tə-rəs; Greek: Τάρταρος Tartaros), in ancient Greek mythology, is the deep abyss that is used as a dungeon of torment and suffering for the wicked and as the prison for the Titans. As far below Hades as the earth is below the heavens, Tartaros is the place where, according to Plato in Gorgias (c. 400 BC), souls were judged after death and where the wicked received divine punishment. Like other primal entities (such as the Earth, Night and Time), Tartaros was also considered to be a primordial force or deity.
 * Due to the guild being composed solely of Etherious, Zeref refers to the guild as his "bookshelf".