This paper considers the material and literary evidence for sundials in medieval Transcaucasia, and asks what they might contribute to our knowledge of interrelations between the cultures of Armenia and Georgia. My presentation constitutes the preliminary stages of a long-term project concerning a neglected subject. The tradition of sundial construction developed early in medieval Transcaucasia: the first dated examples are preserved from the seventh century. By the thirteenth, they routinely appear on the south façades of churches. Although a complete corpus of dials has yet to be attempted (and forms the goal of the projected study), over thirty examples from medieval Armenia alone have been published thus far, a number which surely reflects only a fraction of the total surviving. The sundials are typically (invariably?) of the semi-circular “protractor” format. Protractor dials are much less complex than classical instruments like those on the Tower of the Winds in Athens, which were calibrated according to latitude and showed both the passing of the hours, as indicated by the gnomon’s edge, and also marked the seasons, as shown by the gnomon’s point. Classical diallers understood the axial tilt of the earth and accounted for it in the construction of their devices. If the gnomon were inserted perpendicularly to the wall, as it appears to have been in the Armenian cases, the dials offered accurate readings on two days of the year at the most: the vernal and autumnal equinoxes. Yet mathematical analyses constitute only one approach to the sundial. What do the Transcaucasian sundials reveal about shared attitudes towards time, about the shape of the liturgical day, and about the role of architecture in chronometry? Are sundials in Armenia and Georgia distinct from each other and how? In considering these questions, I hope to offer a new perspective on a longstanding discussion surrounding the relationship of Armenian and Georgian architectural traditions. What happens when the gnomonic evidence is taken into consideration? These questions constitute the first step toward locating Transcaucasian dials within an even wider cultural landscape: the subject of another, future study.