In architecture, symmetry is the reflection of shared forms, shapes, or angles across a central line or point called the axis. Basically, components that mirror each other across an axis are symmetrical. This is one of the oldest and most continuously used ordering principles in architecture. Symmetry helps bind various elements of a structure together into a single, unified whole. It is also commonly used to create a sense of rational order and calm logic. We can look at symmetry on many scales, from the relationship between single details, to the layout of the complete structure, and even to entire urban centers built on a symmetrical grid pattern. ©study.com