Mastering Sorcery is equivalent to becoming a Rune level in a cult. However, unlike a cult, where the path of the runelord, runelady or runepriest is determined, the paths open to master sorcerers are diverse. In practice, many cabals are based upon the progression of a sorcerer to mastery of a given type. But even the more restrictive cabals allow Archimagus because it is focused on greater understanding of magic itself, which is generally what makes someone interested in sorcery to begin with. For example, the Circle of Skulls, a necromantic cult of power-hungry sorcerers who plumb the secrets of death, undeath and the Underworld, only allows members that attain mastery to choose Necromancer or Archimagus.

Mastering Sorcery requires POW 18, the Sorcery skill, and four spells at 90%, as well as the approval of the sorcerer's cabal (if applicable: this has sometimes caused frustrated candidates to leave a cabal). In addition to the other abilities granted by Mastery, a Master Sorcerer chooses a Path for further study. Archimagus is one such path.

Master Sorcerer - Archimagus

Unlike the Elementalist, the Necromancer or the Wizard, each of who specialize in a particular form of magic, the Archimagus is obsessed with understanding magic as a whole and using the entirety of sorcery. Archimagus Spells and Feats of Arms generally have to do with the understanding, control or concentration of the flow of magical energy, locally or more widely.

Archimagi probably originated the Feat: Mind Palace/ Sanctum. But it has long since become more widely known. Indeed, Imperial sorcery is predicated upon the widespread use of the Mind Palace. Archimagi often have elaborate and potent Mind Palaces however, because these magical mental structures hold great appeal for sorcerers who spend so much time ruminating upon the essence of Magic itself.

Archimagus - The Skill: Begins at half of the current Sorcery Skill of the Archimagus.

This skill is used to access any Archimagus ability or spell. It can also be used instead of a Sorcery skill check when the Game Master deems it appropriate, or when the Sorcery Skill is not considered sufficient. Because archmages study all magic, even theurgy, witchcraft and shamanism, the Archimagus skill can be used to give basic information even on these and other magical forms not practiced by the archmage. 

Archimagus Base Abilities:

Upon becoming an Archimagus, you gain the following:

• Your ability to sense magic and its effects using the Sorcery Skill is refined. You can detect magic up to POWx100 Yards distant and automatically can determine the source or type of any magic detected. For very large concentrations of magical energy, you range might be increased by a factor of one, two or three, as determined by the Game Master and reflecting the amount of energy present.
• You can instantly comprehend one enchantment that is imbued in an item or cast upon a person you examine (you must touch the subject of your examination), merely by spending 3 POW and making an Archimagus Skill success. You may do this multiple times in order to learn further enchantments.
• You are more difficult to affect with hostile magic. Variable spells cast against you are automatically reduced by 1 Magnitude. In addition, you add +2 to your POWer when resisting hostile spells that require a POWer contest.
• You can learn Archimagus spells and Feats of Arms.
• You may create a Homonculus Familiar.

Familiar:

An Archimagus can create a magical homunculus, either an ethereal entity, or a corporeal one. An ethereal entity is essentially a magical spirit that the Archimagus brings into being. A corporeal homunculus may be an animal, magical beast, construct or item.

Below are a spell and a couple of Feats of Arms for the Archimagus. Mind Palace is also extremely common among Archmages. Others to follow.

Spells: Archimagus spells are subject to Spell Manipulation.

Channel Energy [Archimagus]      Range – 10 Yards               POW Check – No

Cost to Learn – Research Only

Magnitude – Variable

Time to cast – 1 Action

Duration – 10 Rounds

You can restrict or direct the flow of magical energy in an area. Each Magnitude acts as Countermagic 1 against ANY hostile spellcasting in the affected area. In addition, you can harvest up to 1 POWer per Magnitude of the spell per minute, which you can use for casting within the region, dispense to other spellcasters as if using the spell “Aid”, or use to replenish exhausted POWer Storage crystals in your possession.

Feats of Arms:

Call to Mind – Prerequisites: Archimagus Mastery

Cost: 5 Hero Points.

Your INT for purposes of spell memorization is equal to INTx2. You may also spend a Hero Point to call to mind any spell you know, effectively memorizing it at the expense of un-memorizing a spell or spell of equal total value, with a Archmagery Skill check.

Twin Casting – Archimagus Mastery

Cost: 5 Hero Points

If you spend a Hero Point, you can cast two spells per round for a number of rounds equal to your Manipulation Limit, one as your Major Action, and another as your Minor Action. Your Minor Action spell is cast at your Archimagus percentage, and costs you twice as much POWer to cast.

Note: The latest version of my system for Sorcery and Sorcerers is attached.