Paul built a tower by stacking six identical layers of the shape below on top of each other. What is the volume of his tower? What is the surface area? Paul's tower is an example of a prism because it is a solid and two of its faces (called bases) are congruent and parallel. A prism must also have sides that connect the bases (called lateral faces). Each lateral face must be a parallelogram (and thus may also be a rectangle, rhombus or a square).​