Vitruvius grounds architectural symmetry in commensurable relations among parts and whole. The human body becomes the exemplary diagram: face, hand, foot, forearm and torso correspond through proportional ratios, while the extended figure can be inscribed within circle and square. The iconic idea is not simply anthropomorphism but a theory of measure in which coherence arises from relational correspondence. Methodologically, the passage converts observation into rule, allowing bodily proportion to function as a transferable design instrument for temples. The wider bridge is to classical aesthetics, geometry and architectural pedagogy. Yet the passage also reveals the normative power of proportion: a particular body becomes the standard through which form is judged. Its lasting contribution is therefore double. It establishes architecture as a science of articulated relations while exposing how measurement can transform contingent embodiments into universal models.