Ancient of Days is a remarkable series of "canons and fugues for video" that comprises Viola's most sophisticated structural and metaphorical explorations of time. Mathematical notations of precise time-code editing were applied to construct illustrations of temporal symmetry, duality and transposition — time-based equivalents of musical compositional principles such as counterpoint and serialism. Astonishing temporal interventions — a 180-degree pan gazing downward on a New York City street that progresses from day to night, an image of Mount Rainier in which the foreground and background unfold in different time planes — unfold as symbolic transformations of natural and urban landscapes.