During the course of a year, the path of the Sun among the stars—the ecliptic—passes through 12 ancientconstellations. Because all but one of these 12 constellations represent living things, human or animal, the Greekscalled them the “circle of Animals”—in ancient Greek, kyklos zodiakos, now shortened to zodiac. The one starpattern in the zodiac that doesn’t represent an animal is Libra, the Scales. However, the Greeks considered the starsof Libra to be both a Scales and the Claws of the Scorpion, which follows Libra in the zodiac, so it’s appropriate toinclude it in the circle as well. 

     The Greeks inherited the 12 constellations of the zodiac, as well as the concept of the zodiac as a singularobject, from the Babylonians. (Ancient Babylonia occupied south-central Mesopotamia on the floodplain betweenthe Tigris and Euphrates Rivers; today, it corresponds to southern Iraq.) The concept of the zodiac was closelyrelated to horoscope astrology—the system of predicting a person’s character and future from where the Sun andplanets were in the zodiac at the time of their birth—a practice which also came to Greece from Babylonia, thoughit was a very late development in Mesopotamia. In fact the earliest known horoscope from Babylonia dates only to 410 BC. But by that time Babylonia had been under the rule of Persian kings for over a century. The ancient Persianswere Sun-worshippers, whereas traditionally the Babylonians had used a lunar rather than a solar calendar. Thus,though it was indeed the Babylonians who conceived of the 12 ancient constellations in the path of the Sun as aunit, which the Greeks then called the zodiac, they did so only as late as the 5th century BC under the influence ofPersian Sun-worship.

     Horoscope astrology as we think of it today developed even later: It didn’t attain its final form and greatpopularity until the 3rd century AD, when the social and political dislocations of the decaying Roman Empire madethe powerless multitudes vulnerable to any superstition that promised knowledge about the insecure future and someillusion of control over it.