Though Roman architecture owed so much to the Hellenic world, its principal preoccupation was with the curve, which had been almost completely ignored by the Greeks for centuries. The traditional trabeated construction associated with Greek Classical architecture was to be gradually replaced by the arches, vaults, and domes at which the Romans came to excel. The use of the curve created an entirely new dynamic in architecture. In a Roman colonnade, for example, the viewer's eye can begin at any point on the column and has the option of going up or down and then, when it reaches the architrave, it has the option of moving left or right. Such units, arranged in a series, "proceed across space in leaps . . . conquering distances in a way that is alien to the slower and more methodical march of columns"

Rivoira, G. T. Roman Architecture and Its Principles of Construction under the Empire. Oxford: Clarendon Press, 1925.

Arches also assume a major role in the design of the complex. Centered beneath the sweep of the ramps, the single, deep arched entryway and the open arch above it set the note for the repetition of arched forms in the upper levels. The next, otherwise very plain, level features two small arched doorways as well. Then, in the fourth level where the hemicycles are located there are no arches at all.

Roman temple buildings were ordinarily placed at the heads of civic forums, opposite the basilicas. But some were located within the precincts of their own sanctuaries. At Praeneste the basilica (with accompanying curia, or senate building) is located at the bottom of the steep hillside on which the terraces of the sanctuary rise. In reconstructions the sanctuary has been shown to consist of seven terraces, most of which were connected by steep flights of steps. At the lowest level an arcade set behind the basilica of the forum complex contains the original oracular cave where the lots were cast (Ward-Perkins 35). The third and fourth levels were connected by extended ramps. The fifth and sixth terraces had porticoes along the front, "which once contained shops," or tabernae (Fletcher 221). The sixth terrace was very deep and featured a portico that ran along its sides and rear. At the center of the rear portico a steep flight of steps extended into the terrace and led up to the seventh level. This top terrace was semicircular and only about half the width of the sixth terrace. It featured a small open area in the center of a semicircle of stepped seating. Kostof refers to this seating as "stairs" and says that the wide open area of the sixth level terrace was the setting for ritual dances (206). Above the seating, or stairs, was a portico that repeated the proportion