The Keepers were a powerful hidden sect that secretly controlled The City at one time. few know of their secrets or their collapse several centuries before.
Primal was the source of the Keeper's Glyph magic and spirituality, and they understood Primal needed to be balanced and thus represented the duality of life. Be it power, natural order, the magic of the gods or spirituality, those who profess to know are deeply split between their perspectives on what Primal is.
Primal is everywhere but cannot be directly sensed by most people. Certain members of humanity insist they can feel or 'see' it and thus can understand and use it. Keepers were among this group of humanity.
Our Lady of the Iron Litany Chapel, a former Hammerite chapel, seems to have a hidden Keeper base under its ruins. A much larger compound is underneath the ruins of South Quarter. The upper levels were taken over by Madam Xaio-Xaio and converted into a brothel known as the House of Blossums. The madam is unaware of the hidden library underneath her business, but suspects there is more to the site.
The Keepers were able to contain and control raw Primal and activate it through glyphs, and certain rune stones contained The ability to improve Primal Focus abilities. The ancient ritual books allowed them to turn primal into raw useable energy for their magic but they used it only in small manageable amounts to maintain balance.
The enigmatic Queen of Beggars has a Keeper-like understanding of the Primal from a spiritual perspective, and discusses the importance of maintaining the balance.