Roman Astronomy and Astrology: The History of Celestial Observations in Ancient Rome

The modern world has the ancient Romans to thank for the origins of many modern technologies, conveniences, and ideas, from running water, baths, and republican style government to roads. Similarly, by the 3rd century BCE, the Romans were prodigious monument builders, so much so that the memory of the great Roman Republic and the Roman Empire continues to exist within a cityscape of stone. Rome’s public spaces were filled with statues, arches, temples, and many other varieties of monumental images, and each of these structures had its own civic or religious function. At the same time, most were embedded with stories, messages, and symbolism so that they also tended to function as propaganda.

Roads, aqueducts, and buildings are perhaps the most notable benefits linked to the rise and expansion of the vast Roman Empire, yet the wealth of innovations, discoveries, and significant improvements on many existing methods and practices are also found in numerous areas. What is clear from this breadth is that the Romans were fundamentally pragmatic. Whether they be Greeks, Etruscans, Celts or others, there seems to have been no compunction from the Romans in using, borrowing, or stealing ideas and successfully adapting them for their own specific needs. Their relatively high levels of technology within the ancient world must be largely attributable to this ability, both in terms of access and attitude - the underlying tenet of Romanization was, after all, to assimilate and modify rather than remove and replace.
The development of Roman astronomy was no exception. It evolved over the centuries, embracing the ideas of many cultures as the Romans conquered much of the known world, soaking up knowledge from Asia, Europe, and Africa. Each civilization brought distinct traditions and scientific understanding, and Rome was a bridge, preserving and spreading the concepts and technologies of its conquered lands, including astronomy. For example, After Cyrus the Great conquered Babylon in 539 BCE, he appointed Chaldean astronomers to his Persian court and safeguarded the detailed Babylonian star charts. The skill of predicting eclipses using these historical charts and mathematics passed from the Persians to the Greeks, and finally to the Romans.

It is well-known that the ancient Romans admired and copied Greek culture and knowledge, and Rome embraced Greek astronomy long before conquering all of Greece in 146 BCE, but Julius Caesar adopted, with modest changes, the Egyptians’ 365-day calendar, which they had used for thousands of years. The Egyptians based their calendar on the reappearance of Sirius, the brightest star in the night sky. When Sirius rose, the Egyptians knew it was time for the annual flooding of the Nile, Egypt’s only source of water for their crops. One scholar in Alexandria, Eratosthenes of Cyrene, calculated Earth’s circumference with astounding accuracy around 240 BCE, and after Rome conquered Egypt in 30 BCE, the empire benefited from the skills of several ancient astronomers, including Claudius Ptolemy, an astronomer and mathematician in Alexandria in the 2nd century CE. His groundbreaking work, the Almagest, became the cornerstone of Roman astronomy.

Roman astronomy had practical purposes, like timekeeping, and Roman ships used the stars for navigation. The Romans oriented monuments, temples, tombs, and cities with specific constellations, and like most ancient people, the Romans believed in astrology. They thought the Sun, Moon, planets, and stars influenced human lives and earthly events, and most Romans viewed astrology as a natural extension of astronomy. They gave the names of their deities to the planets and stars, and they thought the stars, moon, and planets had mystical power and represented the deities. Thus, they studied the movements of the stars and planets to discern their personal fortunes and the will of their gods.