During the later half of the first millennium BCE, Babylonian astrologers utilized two separate micro-zodiac schemes that partitioned a single zodiacal sign in different ways. On the one hand, the ‘micro-zodiac of 13’ synchronized the movements of sun and moon, by linking changes in the sun’s micro-zodiacal signs to changes in the moon’s thirteen zodiacal signs of an ideal month. On the other hand, the ‘micro-zodiac of 12’ depicted its twelve micro-zodiac divisions as a microcosm of the twelve zodiacal signs in a more straightforward manner, employed calculations involving the simpler divisor 12 (rather than 13), and extended twelve-part time divisions to spatial dimensions of the sky. I explore the intellectual and cultural contexts giving rise to each scheme, as well as the implications of their adaptation as dodekatemoria (lit. “twelfth parts”) in Greek and Latin sources, as expressed particularly in horoscopes and writings by Marcus Manilius, Paul of Alexandria, and Vettius Valens.
