The twelfth house is the twelfth and last of the houses of the horoscope. It governs seclusion, the unconscious, hidden things, self-undoing, sorrow, confinement, and what works behind the scenes, the sphere of retreat, dissolution, and all that lies out of sight, including, in the older tradition, prisons, hospitals, and secret enemies. It is a cadent house, held to be of the least force, and it was reckoned in classical astrology among the most difficult of the houses. Yet it is also connected with spiritual retreat, compassion, and the surrender of the self. These are the interpretive conventions of the astrological tradition for this division of the chart, in which the twelfth house describes what is hidden, relinquished, or endured in solitude; it closes the wheel opposite the sixth house of work and daily service before the cycle begins again at the ascendant.
Greek astrologers called the twelfth house Kakos Daimon, the Bad Spirit, the grim counterpart to the eleventh house's Agathos Daimon, and held that Saturn has his joy here, one of seven places across the wheel assigned to a planet's particular ease, in a scheme already traditional by the time Vettius Valens was writing around 175 CE. Reckoned in the ancient sources as the single most difficult house of the twelve, it paired the coldest and most restrictive of the classical planets with the house of confinement, hidden enemies, and self-undoing, a combination the later spiritual reading of the twelfth as a place of retreat and surrender has only partly softened. The Hellenistic joys doctrine, largely forgotten in modern practice, offers a harder account of why this house carries such a heavy reputation than its natural ruler alone explains.
Sources A History of Western AstrologyNicholas Campion with Introduction to Astrology (Eisagogika)Paulus Alexandrinus