Ancient Armor is a set of prestige armor art available to all the professions for those who have Nightfall. As with other prestige armor arts, it's only available as level 20 armor.
Note that, while each armor pieces cost 10, Ancient Armor is considered to be ascended armor.
Where to get it
Ancient Armor can be crafted at the Bone Palace by Palmod for 10 and several crafting materials unique to each profession.
Acquisition, detailed view, and customization by Profession
The appearance of hero's armor can be upgraded with Ancient Armor Remnants.
The appearance of hero's armor can be upgraded with a Mysterious Armor Piece.
Other types of prestige armor