Unlike the temples in ancient Greece, Roman temples are not obviously consistent in their orientation. Nor did any great innovations in philosophical cosmology or mathematical astronomy emerge in the Roman world— at least none that are well known to modern historians of science. Roman astronomy, it seems, was more pragmatic in nature, often intimately bound up with prognostication and astrology.
One of the best-known manifestations of Roman astronomy is the Julian calendar. It evolved initially from a simple sequence of indigenous festivals related to the farmers’ seasonal year, then became increasingly formalized as Roman society became increasingly urbanized. At first the civic calendar was based on the phase cycles of the moon, but it faced increasingly serious problems in getting out of step with the seasonal year because of political interference in the process of intercalation. All this culminated in 45 b.c.e. in the switch from a lunar to a solar calendar, dividing the year into twelve “months” that were in fact completely independent of the moon.
The civic calendar aside, there is little doubt that astronomy played a significant role in many aspects of Roman life. Land surveyors, employed all over the empire with simple instruments, needed good astronomical knowledge: this is clear from surviving surveyors’ manuals. Other topics instruct the navigators of commercial ships in navigating by the stars. Sundials were in common use for telling the hour of the day: over thirty were recovered in Pompeii alone.
Astrology, popular among the Romans’ Etruscan predecessors as well as in Hellenistic Greece, had an uneasy relationship with the Roman state at first, but increased greatly in popularity in the second century c.e. with the rise of mystery cults such as those of Isis and Mithras. These were astral religions, and for many people the sun itself became an object of direct worship. Later, these cults came into direct conflict with Christianity.
