Hellenistic Astrology: Rationalizing Fate

Merging Babylonian star worship with indigenous Egyptian astronomy and Greek mathematics and philosophy, Hellenistic astrologers crafted the fourfold technical structure of astrology that weathered two millennia to survive as the foundational elements of modern astrology today.

Published Categorized as History
The Great Library of Alexandria show payrus books arranged carefully by assistants. On a round desk in the left corner people are reading the books. The library looks old and historic.
Artistic Rendering of the Library of Alexandria, based on some archaeological evidence.

When Alexander the Great returned to Babylon, headed back west after having conquered as far as the foothills of the Himalayas, Chaldean soothsayers reportedly warned him that his death was imminent. They may have even placed an ordinary man on the throne of Babylon, hoping he would absorb the brunt of the misfortune, but to no avail. By the evening of June 11th, 323 B.C., the young conqueror was dead, struck down at the age of 32 by disease or poison. He left behind the largest empire the world had ever seen, although it was not fated to outlast him as a unified whole for long. After 40 years of infighting, nominally Greek successor states controlled stretches of land from Macedonia in the west to the Greco-Bactrian and Indo-Greek kingdoms in the east.

The three hundred years that followed, now known as the Hellenistic period, saw Greek people, language, and culture spread to the far corners of the known world and, conversely, the transmission of knowledge and belief systems from east to west in an unprecedented mixing of cultures. It would be this very mixture that would give rise to a new form of astrology, distinct from the omen texts of the Babylonians: Hellenistic astrology.

Alexandria: The Birthplace of Astrology

On the banks of the Nile, Ptolemy, one of Alexander’s commanders and possible half-brother, founded the dynasty that would rule the land of the pharaohs for the next three centuries. Ptolemaic Egypt’s crown jewel was the coastal city of Alexandria, an economic and cultural hub whose state-sponsored library drew intellectuals from all over the Hellenistic world. The library of Alexandria may have contained up to 400,000 scrolls at its peak, as the city commanded a book trade that stretched as far as modern-day Sri Lanka.

The city itself was populated by three principal ethnic groups: Egyptians, Greeks, and Jews, all of whom would contribute to the fomenting field of astrology. The Egyptians had their own indigenous astrology, primarily tied to 36 groups of fixed stars, known as decans, that would be transposed onto the 360-degree Babylonian circle of the heavens and influence the development of the house system. The Greeks would bring their philosophy and mathematics, and the Jews, thanks to an extended imprisonment in Babylon, would bring key concepts of Mesopotamian star worship.

The exact origins of Hellenistic astrology, like much of the period’s history, are shrouded in mystery. Later astrologers would attribute the field’s development to a cast of semi-legendary figures. The most well-known of these, Hermes Trismegistus, is credited with the writing of the diverse Hermetica, a variety of texts that would become the basis for Hermetic philosophy. Though many writers identified him as an Egyptian Greek, this Hermes was probably a semi-diety representing the cultural fusion taking place in Ptolemaic Egypt as a syncretic fusion of the Egyptian god Thoth and the Greek god Hermes. Various Hermetic writings, including 100 aphorisms known as the Centiloquium, discussed astrology, especially in trying to establish planetary rulership over all sorts of things in nature. Nechepso and Petosiris, Egyptian astrologers identified as pharaoh-priests, were credited with a dialogue that espoused key astrological concepts without complex mathematical descriptions. The Jewish prophet Abraham and even Zoroaster, among others, were also listed as proto-astrologers in this emerging art. No full texts attributed to these authors have survived to the current day, but later hellenistic astrologers such as Vettius Valens would cite these figures when outlining the lineage of the field—although even he would complain of the cryptic nature of their writings.

Chances are, however, that many tenants of astrology entered Greek by way of translated Babylonian texts. Both Vitrivius and Jewish historian Josephus refer to Berossus, a Mesopotamian astrologer and historian who founded a school for astrology on the Greek island of Kos, near present day Bodrum, Turkey, at around 280 B.C. Kos was at the time under Ptolemaic control. The island had also become a major center for Hellenistic medicine as the site of the Hippocratic medical school, and this proximity may have contributed to the later role astrology played in the medical practices of the premodern world. At his school in Kos, Berossos was said to have taught students the art of astrology while translating Mesopotamian texts into Greek. The astrologer’s statue reputedly once stood in Athens, its golden tongue symbolizing the accuracy of his predictions.

From the Celestial Sphere to the Horoscope

Whether from the teachings of Berossos or the increased association between Mesopotamia and Greek-speaking peoples, astrology and the cultural significance of the heavens began to grow in the Hellenistic world. Prior to contact with Mesopotamian star worship traditions, Greek astronomy was relatively undeveloped. The Greeks used the stars primarily for naval navigation or agriculture, and so they had identified only a few northern constellations and had only descriptive names for the planets.

There was no association between the Greek pantheon and the celestial bodies; rather, the Greek gods were more akin to your every day, quarrelsome humans, simply with superhuman abilities. Similarly, there was no concept of the immortal soul. But once the Greeks came in contact with the religions of Mesopotamia and Persia, they were quickly won over by the perceived “mysticism” of these eastern faiths. The rise of the fatalistic cult of Tyche, or Fortune, and the mysterious Mithraism, popular in the 4th and 5th centuries B.C., saw Greek worshipers increasingly drawing on eastern depictions of the gods and the cosmos.

By 400 B.C., Plato wrote of the planets in association with the Greek pantheon; Ishtar had become Aphrodite, Marduk, Zeus. The Romans would adopt this system, giving the planets the names they still hold today. The quarrelsome gods of Greece had become planetary deities who could sway human destiny—and, accordingly, whose will could be interpreted through the observation of the heavenly bodies.

The mystic aspects of astrology were relatively new to the Greeks. However, they had a long and developed history of both philosophy and mathematics capable of crafting a systematic art (rather, a protoscience) out of semi-religious star worship. The idea of the celestial sphere was developed as early as the 5th century, and Archimedes was building models of it by the 3rd century. Astrologers continued to use Babylonian arithmetical calculations until the development of trigonometry, but the geometrical model was much easier to visualize and would be perfected by future generations. Eventually, the work of Hipparchus and Ptolemy allowed for precise prediction of planetary positions, and also contributed technical terminology to help pinpoint the celestial bodies. In the most basic rational view, the heavens consisted of positive and negative forces moving in geometric patterns. 

Greek philosophers too had much to say about astrology. Aristotle saw the stars as divine beings and argued that their regular motion could only be explained through some kind of divine intelligence. Plato in turn developed the concept of the demiurge, the intelligent creator who set the planets in motion and whose plans would ultimately be read by that motion. This interrelation became known as “cosmic sympathy” and is most famously characterized by the phrase “as above, so below.” Different astrologers—and critics of astrology—would all cite the prevailing philosophies of their era, from Middle Platonism to Neopythagoreanism as well as Stoicism, the most popular system of belief in the Hellenistic world.

Principal Techniques in Hellenistic Astrology

Regardless of the influence that different contemporary philosophies had on individual astrologers, Hellenistic astrology itself was built from technical terminology and concepts that made it a rationalized system in its own right. All astrologers had more or less the same associations within the fourfold system, still used in modern astrology, of the planets, signs, houses, and aspects. Each planet was given rulership over certain zodiac signs, acting within those signs as a lord in his dominion. Astrologers recognized four major aspects and conjunction, with the sextile (60 degrees) and the trine (120 degrees), plus conjunction, generally considered benefic associations, while squares (90 degrees) and oppositions were generally viewed as negative aspects. Hellenistic astrologers also made use of a system of mutual reception—when two aspecting planets are in each other’s dominion in terms of sign, exaltation, triplicity, decan or bound—that added another layer of nuance to the reading of a native’s chart.

The planets were therefore interpreted in terms of their positions within signs, in relation to each other, and within the 12 houses. Hellenistic astrologers used the whole sign house system until the 2nd century A.D., wherein the whole of the rising sign represented the first house, and all other houses corresponded to the signs as they progressed from the ascendant. The Greek propensity for dualities meant that the idea of positive and negative forces became the system of benefic and malefic luminaries, while signs were classified as either male or female. Each of the four elements was associated with three signs, and the resulting triplicities (for example, Aries, Leo, and Sagittarius as members of the fire triplicity) would have a significant influence of the practice of Hellenistic astrology. Astrologers also considered sect, whether the native was born during the day or at night, as a prominent factor in determining their fate.

Ptolemy, perhaps the most scientific of the Hellenistic astrologers, attributed the four qualities (wet and dry, hot and cold) to the planets, and strengthened the bond between medicine and astrology in terms of sign rulership of different parts of the body. He would also outline a basic system in which the different planets would rule the different periods of an individual’s life, providing an extremely influential rulership structure that would still be a part of the Western psyche in Shakespeare’s time.

The majority of the astrology practiced in the Hellenistic world was natal, concerned with the fortunes and fate of individuals. As in Babylon, mundane astrology remained prominent, as did electional astrology, providing auspicious times for the founding of cities and the like. Limited evidence of a horary tradition survives, although that branch would develop further with medieval and early Renaissance astrologers. Unlike modern psychological natal astrology, Hellenistic astrology was not limited to foretelling the disposition of the native but involved a number of powerful predictive techniques.

Valens, for instance, spends much of his Anthologies expounding different techniques for calculating the length of life, as well as for determining the time-lord of a period in the native’s life. Through a process known as profection, the Hellenistic astrologer could determine when a certain planet in the native’s chart would be “activated” and gain special power over a certain period of the individual’s life. Other astrologers, from Manilius and Dorotheus to Firmicus Maternus, would build on the same agreed-upon principles with their own practices, creating a complex and evolving field that developed thanks to a balance between standardization and innovation.

An Empire is Born

By the 1st century B.C., traces of this system could be found all across the Hellenistic world. Charts from practicing astrologers showcased these new techniques and by the 1st century A.D. a number of manuals on the arts, from the verse of Manilius’ Astronomica to Valens hands-on Anthologies and Ptolemy’s widely influential, if somewhat dry Tetrabiblios, had appeared. These works, despite their differences and innovations, represented a widespread and standardized practice that combined a rationalized form of planetary worship with the most popular philosophies of the day, plus cutting-edge mathematical processes.

From the contributions of disparate cultures, the astrologers of the Hellenistic world had developed a systematic way to determine the fate of the individual. While Greek would remain the scientific lingua franca of the eastern Mediterranean for centuries, a growing power in the west would soon eclipse the Hellenistic successor states of Alexander’s short-lived empire. This new power, Rome, would in turn absorb the cultural and scientific advancements of the Hellenistic world and, with it, astrology. As early as 139 B.C., the Praetorian edict expelled all astrologers from Italy, showing that astrology in Rome was still largely practiced by foreigners. But as astrology in the rising Roman state ceased to be a foreign concept and became a more significant part of life, it began to inhabit a new seat of power.

Astrologers writing in Greek had provided the philosophical and scientific structure that would remain largely unchanged until the early Middle Ages, but it would be the Romans who would give it an unequivocal political status. From the victories of Augustus Caesar until the rise of Christianity, Roman emperors would rule or fall, kill or be killed as foretold by the planetary “dance of the gods.”


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