This chapter re-examines the image of a canopied building supported by columns that often appears as the concluding page to the prefatory paratext to the gospels known as the Canon Tables, which was devised by Eusebius of Caesarea in the early fourth century. A catalogue of surviving examples of the so-called tholos image is provided, followed by an argument that the image is underdetermined and polyvalent, and that it operates together with the rest of the Canon Tables decorative scheme to invite an imaginative response from the viewer. The latter half of the chapter turns to two texts in Eusebius’ corpus to elucidate the way in which he used sacred architecture as a means of mapping the theological truths and ritual activities associated with such spaces. The same approach can be applied to the architectural decorative scheme adorning the Canon Tables, including its richly symbolic tholos, which can be seen as a potent symbol that can be activated through a biblically inspired ekphrasis and used as a ‘cognitive machine’ to theorise Christian knowledge and practice.