This study examines the astronomical and astrological foundations of the ancient Roman calendar, traditionally attributed to King Numa Pompilio. By integrating classical literary sources, mythological frameworks, and precise celestial calculations, the research demonstrates that the early Roman calendar was not a simple pastoral-agricultural construct, but a sophisticated timekeeping system. The underlying 24-year intercalary cycle accurately harmonizes the tropical solar year with synodic and sidereal lunar motions, as well as the 584-day synodic cycle of Venus. Furthermore, the analysis reveals how public rituals, fertility festivals (such as the Veneralia and Matralia), and human life events were systematically aligned with key astronomical phenomena, including solar and lunar eclipses, nodes, and planetary configurations. Ultimately, the work traces these complex astronomical doctrines to an Etruscan lineage strongly influenced by ancient Near Eastern and Mesopotamian traditions, challenging traditional historiographical views regarding early Roman scientific knowledge.