Asperitas, a key term of Hellenistic-Roman art criticism for the assessment of columnar architecture, is anchored in two passages in Vitruvius, which both point to ‘asperity’ as the decisive criterion for achieving an unparalleled, truly eye-catching visual effect. In the best known of the two passages (3.3.8–9), praise is piled on Hermogenes for having systematically established this effect in the design of temples. In fact, he is credited with the invention of the theory (ratio) of pseudodipteral temple colonnades. And this column arrangement, with ambulatories of greatly increased (double) depth around the cella, is supposed to have been invented to provide dignified grandeur (auctoritatem) in its appearance propter asperitatem intercolumniorum: 3.3.9. This visual effect came with the practical advantage that those deep pseudodipteral colonnades also provided rain-protected space for crowds to circumambulate around the temple’s cella (in aede circa cellam). Vitruvius’ other reference to asperitas, in a visual sense, appears in the context of wall-painting (7.5.5), where a certain Apaturios of Alabanda is reported to have created a deceptively dazzling effect propter asperitatem in his rendering of colonnades and temples, so much so that the visual effect of the painting outshone its deficiencies in logic (which, when pinpointed by the mathematician Likynos, the artist hastened to correct: 7.5.6–7). Here we will analyze a reconstructed 3D computer model of Hermogenes’ well-documented pseudodipteral temple at Magnesia in order to tease out the visual effect and on-site experience of that asperitas which is described by Vitruvius in such tantalizing terms.