When a planet rises in the east it can now be seen - and thus it enters the twelfth house. Just so, our first instances of self-expression that we offer into the world are vulnerable and easily defeated, but the effect of their success or failure on our personality is enormous. Pulling some of our energy back into our self to keep it from being defeated or overwhelmed has two results. If we are aware of what we are doing, it becomes our hidden secret. If this process is unconscious, it becomes a rejected aspect of the self. These secrets or repressed aspects of the self form the classical interpretation of the twelfth house.

But what if the immature energy we put into the world isn’t defeated early on? Then it can become a source of strength and a dominant aspect of our personality, and even signify our career. The twelfth house is thus where we build inner strength to overcome limitations, sorrows and fears, and where the individual adapts to the collective. It signifies self-undoing: where we stand in our own way, where we are not free to let ourselves become and be who we essentially already are. It also represents that which is hidden, karma, limitation, confinement, prison, betrayal, sacrifice, hospitals and institutions, nuns and priests, secrets and secret enemies (who may just be rejected aspects of ourselves), initiation, ultimate understanding, and charity given or received.

Astronomically speaking, the twelfth house is that one-twelfth sector of the local sky just above the eastern horizon (see above picture) occupied by planets during the two hours after they rise.

With Mars (your energy, libido, and assertive principle) in your twelfth house of containment and self-undoing, you need to release your energy and not let it remain blocked or bottled up. Your energy tends to work against you when its repressed, inhibited, or even combative. Learning to express your feelings in a non-combative manner, and developing more forms of creative self-expression would be helpful. You may have secret or hidden enemies that accuse you falsely. Since your own plans or motivations are often hidden, you'd make a good strategist. You may have to depend a lot on yourself. If you have any old resentments, let them go.

If Mars is within 10° of the ascendant it is conjunct the ascendant and much of the above interpretation starts to become weaker. If Mars is in the twelfth house AND within 4° or 5° of the ascendant, then it is said to be on the "dark side" of the first house, and it influence will be felt in the first as well as in the twelfth house. The closer a twelfth house Mars is to the ascendant, the more it will be interpreted as though it were in the first house; when less than 3° from the ascendant, a twelfth house Mars expresses itself primarily -- and eventually entirely -- in the first house.