Player characters typically alternate between the role of a magus (plural magi; female maga/magae), and a companion (Consors). Companions are select skilled non-magi who help wizards conduct their affairs (as magi tend to be distanced from "mundanes" due to the effects of their magical "Gift"). Additionally, there are a number of Grogs (usually skilled peasants, often bodyguards or watchmen) who can be controlled by any player. (As of the Third Edition, Grogs are also a viable player 'class'; the Fifth Edition has added an entire supplement dedicated to 'fleshing out' Grogs.) The wizards generally gather in specialized strongholds called covenants, which are often built in places of power. A covenant is typically a 'home base' where the magi are in charge (though they may travel Mythic Europe for reasons of politics, resources, study or even leisure). Some consider the covenant to be the central character of the game, and the official rules encourage troupes to develop the covenant along those lines.
Standard player-character magi belong to the Order of Hermes, a society of magically "Gifted" humans which was inspired in 767 A.D. by the witch Trianoma and magus Bonisagus after the latter developed a breakthrough in communicating and manipulating magic (termed 'Hermetic Magic' for its roots in both the Greek deity Hermes, upon which the ancient Roman Cult of Mercury was based, and the works of the legendary figure Hermes Trismegistus).While magicians at this time were scattered, rarely social and highly distrustful of each other as a rule, two factors strongly favored mutual co-operation. One was Trianoma's political vision of an organization that would unite the Gifted for their mutual benefit. The other was Bonisagus' second breakthrough, the Parma Magica (loosely translated as "magic shield"): a highly efficient and easily taught personal ritual which could allow these disparate individuals and traditions to meet on common ground with some assurance of safety. Over subsequent centuries, with very few exceptions, magi who quit or refuse to join the Order have been hunted down and destroyed, giving the Order a definite monopoly over magical resources within its 'jurisdiction'.
The Tribunals loosely correspond to groupings or portions of modern-day nations; each has a distinct cultural and historical flavor which is expanded in the Tribunals of Hermes series. For example, the Roman Tribunal is a densely populated area with a shortage of magical resources, offering highly politicized plot-lines (both within and without the Order itself); Novgorod features vast areas of harsh wilderness, where pagan tribal warfare and magical beasts are significantly more common than elsewhere.
Some spells involve more than one Technique, and/or more than one Form at once; each Art used in addition to the basic pair is called a requisite. All relevant Art Scores are compared: the caster's lowest Technique and lowest Form are used, reflecting the limiting of the caster's magical knowledge.
All characters (magi, companions and grogs alike) improve their Abilities by applying experience which can be earned through Exposure, Practice, Training or Study. Magic, however, is stressed as a multifaceted discipline with a greater variety of avenues for improvement. Magi are expected to spend months at a time with books and/or laboratory equipment: inventing new spells (or learning or modifying existing ones), strengthening their Arts, enchanting items, and so forth. Ars Magica includes rules for magical research within the game's standard 'advancement' timescale of 3-month seasons.
Lab Projects concern projects to enhance one's repertoire of spells or magical artifacts. All projects have a level of effect to which the character compares their 'Lab Total': Intelligence + Magic Theory ability + sum of a Form and Technique + other bonuses (which may be from local Aura, quality and specialization of lab, assistants, special knowledge, sympathetic connections from items, and in some circumstances an additional Ability). Some merely require a Lab Total to match the Level of Effect; more extensive endeavors simply add up each Lab Total in 'points' until twice the Level of Effect are accumulated. 2b1af7f3a8