Tetrabiblos

Ancient Astrology According to Ptolemy

Ptolemy, in Margarita Philosophica by Gregor Reisch, 1503.

Western astrology counts its origin at least back to Babylonian times. But the primary source to classical astrology and the components of the complete horoscope is Tetrabiblos by the famous mathematician Ptolemy of the 2nd century AD.

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What he stated in his text still stands in the 21st century.

Claudius Ptolemy (c. 90- 168 AD) was a Roman citizen of Greek ascent, famous in the history of science for his accomplishments in mathematics and astronomy. His importance in astrology is usually not dwelled upon in the history books, but the components of our horoscopes stem from his treatise on the subject.

Astrology Bible

Tetrabiblos is the veritable bible of astrology. "Biblos" in the title is the same word as bible, but it really just means book. "Tetra" is four, so the title simply says that it's a text of four books. We would say chapters. It explains quite straightforwardly the components of the complete horoscope — Zodiac signs, planets, astrological Houses, and the major aspects. Ptolemy's explanations as to their meanings have not been altered much since.

Still, like most of the Ancient Greek literature, the text was lost to us until its first translation from Arabic in 1138, after which it spread like a plague. I would say, though, that the teaching of his text was kept alive among astrologers also in the many centuries when they didn't have access to the whole book.

New Planets

Although the basics of astrology as taught by Ptolemy — and he was certainly not the first to pass them on — remain the same, some components have been added since his time.

Ptolemy and his predecessors knew of no other planets than the ones visible to the naked eye, which are the ones out to Saturn. With the invention and improvement of binoculars and telescopes, new planets were discovered: Uranus in the 18th century, Neptune in the 19th, and Pluto in the 20th.

They have been given their astrological meanings much from the "zeitgeist" and world events of the times of their discoveries. Ptolemy knew nothing of them, of course.

Other House Systems

Also, long after Ptolemy's demise, alternate House systems have been introduced. He practiced Equal House, which means 30° for each House, starting from the Ascendant.

Placidus de Titis (1603–1668) invented the House system named after him, which is actually more at use than the Ptolemy Equal House in present time. It puts the cusp of the 10th House at the MC (Medium Coeli) and allows for different sizes of the Houses.

Johannes Regiomontanus (1436-1476) had done so more than a hundred years previously, but his slightly different House system is not that common today.

Minor Aspects

Ptolemy mentioned only the five major aspects in his Tetrabiblos: the conjunction, the opposition, the trine, the square, and the sextile. Since then, several others have been introduced, such as the quincunx (150°), the quintile (72°), and on and on.

Although the aspects have multiplied, there is still consensus among astrologers about the five Ptolemaic aspects being the most important ones.

Apart from these later discoveries and inventions, Ptolemy's horoscope definitions remain.

Get the book

The image to the right is a link to the Amazon page for Ptolemy's Tetrabiblos in the Loeb series. There are several translations of the book, but as with all the Greek and Roman classics, the Loeb Library contains the most trustworthy and authoritative translations.

If you are interested in classical astrology, I recommend reading Ptolemy. You will find just how little has really changed through the many centuries. His writing is quite clear and definitely sharp, so you will enjoy it. When you've read Tetrabiblos, you are right at home with all the Western astrologers through the centuries since the days of Ptolemy. They all based their horoscopery on his principles. We still do.

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