Despite being one of the most recognizable buildings from ancient Rome, the Pantheon is poorly understood. While its architecture has been well studied, its function remains uncertain. This paper argues that both the design and the meaning of the Pantheon are in fact dependent upon an understanding of the role of the sun in the building, and of the apotheosized emperor in Roman thought. Supporting evidence is drawn not only from the instruments of time in the form of the roofed spherical sundial, but also from other Imperial monuments, notably Nero's Domus Aurea and Augustus's complex of structures on the Campus Martius -his Ara Pacis, the 'Horologium Augusti,' and his Mausoleum. Hadrian's Mausoleum and potentially part of his Villa at Tivoli are drawn into this argument as correlatives. Ultimately, it is proposed that sun and time were linked architecturally into cosmological signposts for those Romans who could read such things.