Tartaros

Tartarus (冥府の門, タルタロス, Tarutarosu) is 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 Walrod Cken, they may have one of the Books of Zeref in their possession.

Location and Building
The Tartarus 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 Tartarus 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, one of Tartarus' core members, described the entire building as "a sickening piece of architecture".

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 Tartarus are Demons from the Books of Zeref, with the strongest Demon, E.N.D., being their leader.

Trivia

 * Tartarus, in Greek mythology, is a deep, gloomy place, a pit, or an abyss used as a dungeon of torment and suffering that resides beneath the underworld.