The Fault in our Stars: Marcus Manilius and Western Astrology

As the Roman Empire rose, absorbing the trappings of Hellenistic culture, one writer penned the oldest surviving complete treatise on the art of astrology. Part poetics, part mathematics, Manilius’ Astronomica offers a glimpse of the core concepts and Stoic philosophy underlying both Hellenistic astrology and the beginning of modern Western science.

Published Categorized as History
Opening page shows intracate design on yellow background with text in brown.
The opening page (top section) of the poem Astronomica by the Roman poet Manilius

At our birth we begin to die, and our end depends on our beginning

– Marcus Manilius, Astronomica, trans. Thomas Creech

Shortly before the beginning of the Christian era, the Roman Republic underwent a series of monumental shifts. The assassination of Julius Caesar on the infamous Ides of March, 44 B.C., threw the republic into a civil war, from which it emerged in 31 B.C. as an empire under the rule of Augustus Caesar.  

These political shifts came with other changes in the Roman world, notably the rise in the prestige of astrology. A proto-scientific form of divination, Roman astrology was built on Greek, Babylonian, and Egyptian astronomy and mathematics combined with aspects of the Roman polytheistic pantheon. It was during the reign of Tiberius, the second Roman emperor, that the oldest surviving comprehensive astrological text was written: Marcus Manilius’ Astronomica. Very little is known about Marcus Manilius himself, except that he was a poet, mathematician, and astronomer. Astronomica is his sole surviving text, and much of what we know about the poet can be derived from the text itself.

Like Lucretius’ Epicurean text De rerum natura (On the nature of things), Astronomica is a lengthy didactic poem written in hexameter. Unlike its Epicurean counterpart, Manilius’ text focuses on what was then the cutting edge of Roman astrology, all told from a distinctly Stoic perspective of the universe. While not as well-known as Roman poets such as Virgil, or as famous as prominent astrologers such as Ptolemy, Manilius nonetheless produced a text that managed to summarize complex mathematical procedures in verse while laying the groundwork for what would become modern Western astrology. By delving into the style, content, and worldview of this fundamental text, the reader will come to understand how the verses of Manilius’ Astronomica still echo in our collective understanding of astrology today.

Roman astrology in the first century A.D.

Prior to Augustus’ reign, the Roman’s primary methods of divination involved observing the flight of birds, known as augury, and examining the livers of sheep, known as haruspicy. During the rule of Augustus and his successors, however, the importance of astrology within the empire blossomed, with many emperors having their own court astrologers. Augustus himself prominently featured the symbols of his astrological sign, Capricorn, in palatial art and even coins. In contrast to earlier, animal-related divination methods, astrology used rigorous mathematical analysis to provide emperors, among others, with valuable predictions about their fortunes, their projected lifespan, and even the chain of imperial succession. It was perhaps this feature that underpinned the influential role this formerly Greek divination practice began to play in the Roman Empire.

Few astrological texts predating Astronomica survive, the most notable being the Hermetic Writings, horoscopes penned by an anonymous astrologer 100 years before Manilius’ seminal work. Similarly, while Manilius does not include example horoscopes in Astronomica, neither the basic form used by preceding astrologers nor the precursor of the modern natal chart first used by Byzantine astrologers, the geometry of the circle of the Zodiac and its subdivisions plays a large role in the work.

Astronomica: Structure and Key Concepts

Astronomica consists of five mostly complete books, with one extended passage in the fifth book lost to time, though some experts speculate that the initial work could have been up to eight books in length. Three key features demonstrate the maturity of the field of astronomy at the time of Manilius’ writing. First, the identification of astrological positions around the ecliptic; second, clear rules for interpreting those positions; and third, the use of technical terminology.

The first book begins by outlining Manilius’ concept of the universe, which he defines as being created out of the four elements, ruled by a divine spirit and governed by reason. It then delves into the Greek model of the heavens, upon which Manilius and many other early astrologers based their investigations. This model involved two spheres, the first being the Earth, at the center of the universe, and the second being the firmament, the hollow sphere upon which the stars were thought to be fixed. The Sun, Moon, and planets were said to revolve around the Earth in the space in between the two spheres. The first book concludes with a discussion of constellations, comets, and the origin of the Milky Way.

From Andreas Cellarius Harmonia Macrocosmica, 1660/61. Chart showing signs of the zodiac and the solar system with world at centre.
Scenography of the Ptolemaic cosmography

In book two, Manilius begins to discuss the characteristics of the 12 signs of the Zodiac. He does so in part by linking the sign to its symbol: Aries the Ram, Taurus the Bull, and so forth. The signs are further classified as masculine or feminine (in line with the Hellenistic notion that odd numbers are masculine and even numbers are feminine) as well as hot or cold, moving or fixed, and even nocturnal or diurnal. Interestingly, he proceeds to delve further into each sign’s characteristics based on their Olympic protectors. This too differs from modern astrology, as most later astrologers would focus more on the planet associated with each sign rather than the Roman deity. In Manilius’ conception, the god of war, Mars, was the patron of Scorpio, whereas Aries, more commonly associated with the planet Mars in later astrological practices, was associated with the Roman goddess Minerva. Manilius also links each sign to a certain section of the body in a diagram commonly known as the Zodiac Man. This key concept likely predated Astronomica but played a significant role in medical practices prior to the emergence of scientific empiricism. Manilius then presents the concept of aspects or significant angles within the birth chart. Points on the ecliptic within 10 degrees of each other are said to be in conjunction, whereas a 60 degree angle between two points represents harmony and a 90 degree angle represents conflict. Further important angles include the sextile, a 120 degree angle, and opposition when two point face each other across the chart. Each of the 12 signs is also divided into a further 12 parts, known as dodecatemoria, each consisting of 2.5 degrees of the ecliptic.

The second book ends with a discussion of the fixed circle of the observer and the dodecatropes, 12 sections of the ecliptic dependent on the observer’s location and time that later became what are currently known as houses. Manilius’ text is the first notable work to mention the system of houses, which he called templa,although he merely gave each generic positive or negative associations. A century later, Vettius Valens would outline the concepts now associated with each of the houses.

The third book, considered the most mathematically complex in Astronomica, is mostly dedicated to the discussion of sortes, also known as lots, significant positions on the natal chart. The most important of these was the ascendant, or the sign rising on the horizon at the time of the horoscope. Interestingly enough, it wasn’t until the 20th century that astrologers began to prioritize the sun sign over the rising sign in horoscopes. Other important lots included the descendant, the aptly named lot of fortune, and the prorogator, which was used to calculate a subject’s projected life span.

Opening page shows brown text on yellow background with intricate blue design on left
The opening page of the poem Astronomica by the Roman poet Manilius.

The fourth book delves into a number of concepts originating in Egyptian astrology, especially decans. Consisting of 36 groups of stars located south of the ecliptic, decans were used to calculate time in ancient Egypt and gradually became deified, eventually being portrayed in Islamic art. The fifth and final book recounts the myth of Andromeda and Perseus, notable for containing a number of characters immortalized as constellations. Manilius uses the myth to explain the significance of paranatellonta, stars that rise simultaneously with a given zodiac sign. These stars, such as the Hyades, helped astrologers calculate horoscopes even in the event of cloud cover. He ends the work by meditating on the elaborate structure of the heavens that allows the astrologer to see the workings of fate, which he attributes to the divine intelligence ruling the universe.

The Influence of Manilius on Western Astrology

In the coming centuries, many Greco-Roman scholars, including Vettius Valens and Claudius Ptolemy, would build upon and expand the concepts first outlined in Astronomica. The text itself languished in relative obscurity during the Middle Ages, and was first rediscovered in 1416 by Poggio Bracciolini, an Italian humanist. It was translated into English in 1697 by Oxford-educated poet and translator Thomas Creech. Manilius is often associated with famous classicist AE Houseman, who spent the first thirty years of the 20th century editing Astronomica and is largely responsible for bringing the Latin poet to the attention of Western scholarship. In 2009, Katharina Volk published Manilius and His Intellectual Background, the first English language text on Manilius and Astronomica. While the concepts outlined by Manilius arguably form the foundation of Western astrology, Astronomica is not widely read, likely because of the complex mathematical nature of the text. Nevertheless, a few key features point to the way in which Manilius’ writings influenced contemporary concepts of astrology.

The first, a product of the complex mathematical nature of Astronomica, is the composition of the natal chart. Many of the key features that Manilius outlines in the second and third books are recognizable even to amateur astrologers today. A circular chart with two layers, the outermost, representing the 12 signs of the zodiac, revolving around the innermost, representing the 12 mundane houses, which are fixed based on the position of the observer, is the basic outline for any contemporary horoscope. While the main qualities associated with both Zodiac signs and the mundane houses have developed considerably since Manilius, the basic layout remains the same. Accurate calculations of the boundaries between signs and houses remained mathematically impossible until the works of Ptolemy a century later, and most contemporary astrologers use ephemerides, or precalculated tables, today, as using different mathematical processes can still yield different results. Manilius also set forth the division of the birth chart into quadrants via lines connecting the ascendant and descendant and the midheaven and the immum coeli, or lower midheaven. The system of aspects, or key angles existing between two or more points on the ecliptic, is still in use as well.

The second vital feature of Manilius’ text has to do not just with its content but with the worldview he espouses. Considered by many classicists an inherently Stoic text, Astronomica is written with the assumption of a divine, reasoning creator that rules the universe through an orderly system of cause and effect. Similar to Plato’s concept of cosmic sympathy, Manilius asserts that the careful observer can make sense of the order of the universe by observing its natural features. Indeed, as he writes, “nature is nowhere concealed”. While this worldview reinforces a sense of fate and interconnectedness, it also encourages further investigation of the natural world in search of knowledge. While astrology is considered a pseudo-science by some today, astrologers in the 1st century A.D. employed the cutting edge of mathematics and astronomy to construct birth charts.  In fact, Poggio Bracciolini may have looked to Manilius’ text primarily as a source of information about comets and other celestial bodies, at a time when the Greek model of the universe was being called into question. As mentioned earlier, the diagram of the Zodiac Man was also a significant resource for physicians prior to the advent of modern medicine.

While not as well-known as works by contemporary poets like Lucretius, or as fully developed as later astrological writings, Marcus Manilius’ Astronomica nonetheless lays the groundwork for contemporary Western astrology. By outlining key terms and plotting the geometric organization of the natal chart, as well as introducing the major aspects and the system of houses, Manilius gave astrologers vital tools still in use today. Furthermore, by examining the world around him in a manner both artful and rigorous, he arguably espoused a worldview that called for the continual advancement of scientific knowledge, using whatever tools are available to the observer.


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