NB: For this Ars Magica node, I am working from my experience primarily with 3rd edition texts and gaming, but from a few 4th edition texts as well
"Salvete sodales, it is my pleasure to make your acquaintance. I am Ellylldan, Magus of House Merinita. I understand that you wish to learn something of Sedes Silva, our covenant, yes? I see that you are not yourself of the Order, so perhaps you are seeking employment here among the turb? No, you have a manner of education and edudition... you must be seeking a place as a consors, then? But you seem confused, still. Let me show you around, then, and tell you of our fine covenant...
"The covenant ... no, the word 'coven' is only used by the ignorant peasantry, and smacks too much of the diabolism we hate even more than do they; you should not speak that word again. Covenant, yes, that is the word, from the Latin convenium, a pact — originally it referred only to the charter that earlier Magi made among themselves for mutual protection, mutual aid, and shared learning. But, over time, Magi came to broaden the term to refer to the group of allied Magi themselves, and by extension the place where they live, work and study together, along with their apprentices, consortis, and grogs.
"This wonderful village, hidden here in the woods, is the covenant to which I now belong. No, you could not exactly call it typical; I'm sure there is no such thing in the whole Order of Hermes, at least in terms of the covenant's location and manner of construction, though certainly all covenants have some characteristics in common. All, most likely, provide living quarters and laboratory space for the Magi, some sort of library, and accomodations for the others who assist and serve us."
The word "covenant" in the Ars Magica role-playing game is used to refer both to "a durable group of associated and ostensibly allied Magi" and the place this group considers its headquarters — the latter can take any number of forms, depending on the size and shared resources of the group; e.g., it might be a single, fairly typical Medieval structure or set of buildings, a tower, a castle, a series of caves, or even a caravan of wagons or a ship.
The Covenant is, in many ways, the most important "character" within the game. While it is not (generally) capable of independent thought, and does not take independent action, nevertheless it greatly influences the game, providing a backdrop for the action of many stories as well as filling the downtime for Magi between stories; providing a rationale for the characters to live together and be a cohesive group; and provides a common set of goals and interests. Finally, as Magi, Companions and Grogs come and go, live and die, the Covenant provides the single most enduring presence in the game; it gives the game its overarching identity.
Most Covenants enforce an initiation upon new aspirants. This initiation, which varies in form and length from Covenant to Covenant, almost always ends with an oath spoken by the new member to the entire Covenant population, both magical and mundane.
Excerpts from a Typical Oath
As composed by Consuelia, founder of Mistridge Covenant, in the year 1067...
"I, [name] of House [name], do humbly ask for acceptance into the Covenant of Mistridge. I do so of my own will, under no influences other than my own; no magicks or powers mundane force me here today. I undeersand that my life is forfeit should this or any other part of my oath be found false....
"I here truthfully state I have never consorted with or aided demons, diabolists, or practitioners of magic other than those sanctioned by the Order....
"I swear to follow both the Code of Hermes and the Peripheral Code, lest I lose my title of Magus, position within my House, and place within this Covenant....
"In all respects I will uphold the reputation and honor of this, my new home, and consider its welfare above my own...."
"As I noted, ours is but a young covenant, barely a few years into its Spring. Yes, Spring. You are not familiar with the famous Dionasian treatise, then?"
"Well, then, we have come to understand that Covenants, just as people, have a life-cycle, and we often use seasonal concepts and names to describe this cycle. The Magus Dionasius of House Bonisagus wrote a famous treatise, The Changing Seasons of a Covenant, in which he detailed a new way of understanding the Covenant. I will see if the librarian can secure a copy for you..."
Excerpt from The Changing Seasons of a Covenant
"A covenant begins in Spring upon its founding and throughout it attempts to establish its presence in a region. After a covenant has achieved some measure of power and stability, it moves into Summer, during which it comes into its prime of strength and vitality. Autumn marks the beginning of the covenant's decline, but in this stage it has great political influence and reaches its highest status. The power won during Summer is maintained, and the covenant's influence begins to be used for good measure, but decadence and sloth set in. Finally the covenant decays into Winter, a time when it has lost its power, reputation, and influence, but still clings to the shadow of life...
"Some Winter covenants with determined and dedicated leaders or an influx of new blood may revive and start the cycle anew with the onset of a second Spring, but often the decay is too ingrown to be reversed. Many covenants simply fade away after the long darkness of Winter..."
Covenants are created, much as are characters, but usually through the cooperation of the entire troupe. A template is chosen for the season and style of the Covenant, and various attributes are chosen, purchased or rolled, just as Characteristics, Virtues and Flaws, and Abilities were generated for player characters.
As the game progresses, players may use their resources to upgrade the Covenant, e.g., acquiring a better Hermetic library, hiring additional Grogs or Companions, developing relationships with local powers and/or political influence of their own.
"I must be on your way. I have matters to attend to in my laboratory, and dare not leave my young apprentice alone any longer. If you wish to know any more, just ask the librarian, Eve Rything. Eve will assist you as best she can in finding the appropriate resources."