This paper deals with the function and meaning of sundials in Early Modern Rome, more specifically in gardens. It concentrates on two gardens, both on the Quirinal hill and directly facing each other: the papal gardens of Monte Cavallo and the Jesuit garden of the Noviciate of Sant'Andrea del Quirinale. Set on each side of the magnificent Via Pia, these gardens represented two intersecting yet contrasting worlds, a rude juxtaposition of one cosmos clashing against another: that of a Jesuit community and that of the Papal court. Each had developed a specific language to articulate their main concerns and proclaim their truths to garden visitors. By drawing a contrasting picture of the S. Andrea garden and the Papal gardens, in which sundials were given very different meanings, the intent of this paper is to probe the awkward, contradiction-ridden, spinoso relationship between religion, science and curiosity in Early Modern Rome. In 1685, the Dutch civil engineer Cornelis Meyer devised a method to re-erect the obelisk of Augustus, which had formed part of a famous ancient sundial known as the Horologium Augusti. Published in a book on hydraulic engineering, Meyer's method was supplemented by an entire section in which he explained how one could transform Rome's piazze, with their obelisks and columns, into colossal sundials. He suggested that the obelisk be erected on Piazza Monte Cavallo on the Quirinal hill and that the monument be given back its ancient gnomonic function (Fig. 1). Meyer's elaborate gnomon would determine the hours of the night through the use of the same type of pierced gnomon that would be used a century later, in 1792, when the obelisk was finally erected on Piazza D. Ribouillault (*) Département d'histoire de l'art et d'études cinématographiques,