The main focus of this research project was Renaissance planetary horology. The narrative of the Scientific Revolution rests on three major buttresses: a new astronomy, a new empirical method, and a new mathematical abstraction for explaining a mechanical world. Renaissance clockmaking encompassed these three areas and challenged both the best university-trained mathematicians and the best “superior-craftsmen.” This was especially the case in planetary clockmaking, a branch of the craft that represented both the motion of all the known seven heavenly bodies (Moon, Mercury, Venus, Sun, Mars, Jupiter, and Saturn) and the sphere of the fixed stars. Planetary clocks were an analogical representation of the Universe, as it was known before Galileo’s observations. Renaissance planetary horology, because it was based on Ptolemaic astronomy and was relevant for medical astrology and for horoscopes, has been largely neglected by mainstream narratives in the History of Science and Technology, which are more interested in the genealogy of clocks as chronometers than as cosmological instruments. Yet, planetary horology was the field where the best artisanal knowledge and the most refined scholars came together and experimented on the mechanical reification of the Ptolemaic system of the world. Planetary clocks were the most complex and expensive mechanical objects of Renaissance courts: their design and construction demanded several years’ work by highly specialized craftsmen and mathematicians, and only powerful patrons could fund such enterprises. The history of planetary clocks is indivisible from the concept of the court, which attracted the best urban superior craftsmen and university trained mathematicians. The history of planetary clockmaking is a narrative of how princely powers competed, how confessional differences interacted with the making of science, how medicine dominated mathematical theory and practice, and how the construction of machines that are today almost forgotten broke down, at court, the old epistemological boundaries.