What architectural plan is employed in the Temple of Portunus?

The Temple of Portunus utilizes a pseudoperipteral plan, which is characterized by a rectangular cella (inner chamber) surrounded by a colonnade on the front and sides, giving the illusion of a fully peripteral structure. In this arrangement, the temple mimics the appearance of being surrounded by columns while, in fact, it has engaged columns (or pilasters) along the back and sides instead of freestanding columns.

This design choice blends Greek architectural influences with Roman innovation, where the function of the temple and its aesthetic representation are harmoniously combined. The use of a pseudoperipteral plan allows for a more dramatic play of light and shadow, enhancing the visual impact of the façade while maintaining structural integrity and economic use of space.

The other architectural plans mentioned do not accurately describe the Temple of Portunus. A peripteral plan features freestanding columns all around the cella, a hypostyle plan has a roof supported by numerous columns typically forming a large hall, and a cella plan refers specifically to the inner sanctuary of a temple itself, not its overall layout.