The sixth house is the sixth of the twelve houses of the horoscope. It governs work and daily service, routines, health and illness, and, in the older tradition, servants and small animals, the sphere of duty, maintenance, and the ordinary labour by which life is kept in order. It is a cadent house, held to be of lesser force, associated with the mutable, transitional phase of its quadrant. In classical astrology it was reckoned one of the more difficult houses, connected with hardship and sickness. These are the interpretive conventions of the astrological tradition for this division of the chart, in which the sixth house describes the demands of work and the condition of the body; it stands opposite the seventh house of partnership only obliquely, its true opposite being the twelfth of seclusion across the wheel.
Greek astrologers named the sixth house Kake Tyche, Bad Fortune, the direct counterpart to the fifth house's Agathe Tyche across the chart, and the Hellenistic scheme that fixed this pairing, already traditional in Vettius Valens around 175 CE and systematised by Paulus Alexandrinus in 378, held that Mars has his joy here, one of seven places assigned to a planet's particular ease. The name is unambiguous about how the tradition regarded this house long before illness and daily labour became its standard modern description: it was a place of ill fortune outright, and Mars's joy there, the planet of cutting, wounding and forced effort, reinforced a reading of the sixth as a house of struggle, the body's vulnerability and the servant's toil, rather than the more neutral routine and maintenance later astrology tends to emphasise.
Sources A History of Western AstrologyNicholas Campion with Introduction to Astrology (Eisagogika)Paulus Alexandrinus