Pisces is the twelfth and last sign, mutable, watery and ruled in the classical scheme by Jupiter, with Venus exalted in it; modern astrology commonly substitutes Neptune, discovered in 1846, a reassignment less than two centuries old. The sign closes the zodiac at the end of winter, immediately before the vernal equinox returns the cycle to Aries, and its traditional meanings turn on dissolution and the loss of boundary: the ending of things, the merging of what was separate, confinement, retreat and what is done unseen. The twelfth house, which corresponds to it, carries hidden enemies, imprisonment, hospitals and self-undoing in the older texts. It is a bicorporeal sign, figured as two fishes, and is classed among the fruitful signs in questions of fertility.
Pisces's three decans run Saturn, Jupiter, Mars, completing the thirty-six-decan cycle that began at Aries; because thirty-six is not evenly divisible by seven, the sequence does not return neatly to Saturn at the true starting point of the cycle, a small mathematical untidiness the Chaldean decan scheme simply accepts rather than corrects. As the last of the water signs, Pisces closes out the same triplicity dispute already discussed under Cancer and Scorpio: Ptolemy's table gives Venus by day and the Moon by night with Mars as co-ruler, while the Dorothean table Lilly transmits assigns the whole triplicity to Mars alone; because Jupiter, not Mars, rules Pisces itself in the classical scheme, the two tables produce a more noticeably different dignity picture here than they do for Mars-ruled Scorpio.