The metaphysical concept of time was a source of delight for medieval artists and patrons alike, inspiring illuminations that showed the stars, the seasons, and the cyclical return of sacred days. Books of hours with decorated calendar pages were especially popular among Christians in the 14th and 15th centuries; the most lavish examples included the Signs of the Zodiac and the Labors of the Months, which had also appeared in Jewish art tracing back to the early Middle Ages. Whether in the Jewish mahzor or the Christian sacramentary, the careful organization of ritual time was a central theme of religious books; even the ostensibly secular books in this section present star charts and images of the celestial sky to link their readers to the distant biblical past and the expected eschatological future.Tracking time had obvious practical advantages, guiding agricultural practices and allowing people to plan for the changing seasons. More fluid meanings of time, however, were also always present as medieval people looked to the ancient world for inspiration. Zodiac signs and astrology had applications for medieval science and medicine; the Labors of the Months offered idealized glimpses of working life for the aristocracy, who observed the ploughing and reaping of the fields from a privileged perspective, but also remained mindful of the greater themes that linked their worlds: mortality, religion, and power bound within moments of time.