What is a Decan (why are decans associated with the Minor Arcana) and how is a decan shown in GD Tarot artwork?

A question asked in the Sanctuary of Mau (Golden Dawn Facebook group for people working their way though the Cicero's Self-Initiation into the Golden Dawn Tradition textbook):

BB wrote:

"I'm trying to draw the two of Wands now, but I'm a bit confused by the wording. What does "Two small wands above and below" mean? I'm supposed to draw two central ones being held, then two above and two below them, making for six wands total? And what is the Decan? Maybe I should put this project on a hold until I have a better grasp of the material."

Description from Book T: "A WHITE Radiating Angelic hand, issuing from clouds, and grasping two crossed wands. Flames issue from the point of junction. On two small wands above and below, with flames of five issuing therefrom, are the symbols of Mars and Aries for the Decan."

My answer:

The small wands are just places to stick the symbols of Mars and Aries. Most, if not all, modern artists ignore that part of the description and just use the astrology symbols. If you really want something to place them on, I suggest little banners.

The small cards (Minor Arcana) two to ten in the sutis are associated with the Decans. A Decan is a third of a Zodiac sign (ten degrees). [Some other occult sources use the term Face for them.] Each Decan has a sub-ruler that flavors that ten degrees, and is stronger when you find the planet there. The typical wording is "planet in sign," but really should be "the ten degrees of the sign subruled by XYZ planet."

There are two ways to assign the planetary subrulers to the Decans. The method used by Golden Dawn is based on the same pattern as the assignment of the planets to the Tree of Life sephiroth. The other method (sometimes called the Vedic method) is based on the element of the sign and the rulers of the other two signs of the same element; this alternative method is actually easier to figure out in your head. Due to Golden Dawn choosing the harder method, it helps the reader if the astrological symbols are on the cards to remind the reader of the card's assignment.

So how is the decan used in readings? Besides being one of several layers that make up a card (others being Number, Colors, Sephiroth, etc.), one can use it to determine timing (this event will occur while the Sun is in this ten degrees of the Zodiac), and also the placement of planets when one does readings based on the planets.

For instance, in a Planetary based reading, the first card pulled would be the position of the Rising Sign, the second would be the position of the Sun, the third would be the position of the Moon, etc.

An example of the Two of Wands done by a modern artist and Adept.

Assignment of the Decans to the Minor Arcana.