The use of architecture as a visual and conceptual frame is well attested in medieval art. For example, in medieval illuminations, architectural frames are often used to separate images from the accompanying texts. Such architectural 140 frames signify potent transparent boundaries between the space of the beholder and the space of that which is seen and, therefore, define perceptible liminal spaces. Actual architectural frames and their role in defining sacred space, however, have been studied far less.