Scorpio is the eighth sign, fixed, watery and ruled in the classical scheme by Mars; since the discovery of Pluto in 1930 much of modern astrology has assigned it a second or substitute rulership by that body, a change that is barely a century old and should be dated as such rather than read back into the tradition. No planet is exalted in Scorpio, and the Moon takes its fall there. The sign occupies the depth of autumn, when growth has stopped and decay has begun, and the traditional readings follow: dissolution, what is hidden, what is inherited from the dead, and the fixed water that does not disperse. The eighth house, which the sign corresponds to in the natural chart, carries death, legacies and other people's resources, and the interpretive overlap between sign and house here is one of the tightest in the system.
Scorpio's three decans run Mars, Sun, Venus, continuing the Chaldean sequence from Libra's final Jupiter decan. As a water sign, Scorpio's triplicity is exactly the point of dispute already noted under Cancer: Ptolemy's own table gives Venus by day and the Moon by night, with Mars as subordinate co-ruler, while the table Lilly inherited from Dorotheus assigns the whole triplicity to Mars alone regardless of sect. Scorpio is the one water sign where this disagreement is least consequential in practice, since Mars already rules the sign itself in the classical scheme, so a horary judgment of a Mars-ruled planet in Scorpio comes out much the same under either table even though the formal dignity differs.