The form of Roman temples derived from Etruscan prototypes. Like Etruscan temples, Roman temples were frontal with stairs leading up to a podium and a deep portico filled with columns. They are also usually rectilinear and the interiors consist of at least one cella, which contained a cult statue or image.
If multiple gods were worshiped in one temple, each god would have its own cella and cult image. For example, Capitolia, temples dedicated to the Capitoline Triad, would always be built with three cellae, one for each god of the triad: Jupiter, Juno, and Minerva. Roman temples were typically made of brick and concrete and then faced in either marble or stucco. Engaged columns (columns that are decorative and not needed for structural support) adorn the exterior sides of the temples. This creates an effect of columns completely surrounding a cella, an effect known as psuedoperipteral (Figure 1). This technique is most often seen in Greek peripteral temples. The altar of the temple, used for sacrifices and offerings, always stood in front of the temple.
While most Roman temples followed this typical plan, some were dramatically different. At times, the Romans erected round temples that imitated a Greek style. Examples can be found in the Forum Boarium in Rome, at Hadrian’s Villa in Tivoli and, most famously, the Pantheon at Rome, also built by the emperor Hadrian. The first two examples are very similar to round Greek temples, while the Pantheon’s plan includes a deep colonnaded porch that gives one the illusion of entering a normal rectilinear temple until you walk inside.
The Romans perfected the recipe for concrete during the third century BCE by mixing together water, lime, and pozzolana. The volcanic ash was mined from the countryside surrounding Mt. Vesuvius. Concrete became the primary building material for the Romans and it is largely the reason that they were such successful builders. Most Roman buildings were built with concrete and brick that was then covered in façade of stucco, expensive stone, or marble. Concrete was a cheaper and lighter material than most stones used for construction, which helped the Romans build structures that were taller, more complicated, and quicker to build than any previous ones. Once dried, concrete was also extremely strong, although flexible enough to remain standing during moderate seismic activity. The Romans were even able to use concrete underwater, allowing them build harbors and breakers for their ports.
The Romans effectively combined concrete and the structural shape of the arch. These two elements became the foundation for most Roman structures and building types. The structure of an arch is incredibly solid and strong. It can bear immense weight as it is designed to redistribute weight from the top of the arch to its sides and down into the ground (Figure 3). While the Romans did not invent the arch, they were the first culture to manipulate and readily rely on its shape.
The arch is a shape that can be manipulated into a variety of forms that create unique architectural spaces. Multiple arches can be used together to create a vault. The simplest type is known as a barrel vault (Figure 2). Barrel vaults consist of a line of arches in a row that create the shape of a barrel cut in half. When two barrel vaults intersect at right angles, they create a groin vault. These are easily identified by the x-shape they create in the ceiling of the vault. Furthermore, because of the direction, the thrust is concentrated along this x-shape, so only the corners of a groin vault need to be grounded. This allows an architect or engineer to manipulate the space below the groin vault in a variety of ways.
Arches and vaults can be stacked and intersected with each other in a multitude of ways. One of the most important forms that they can create is the dome. This is essentially an arch that is rotated around a single point to create a large hemispherical vault. The Pantheon is the most famous of Roman domes. The center of some domes is a large round window, opened to the sky. This is known as an oculus (Latin for eye) and it lets in light, rain, and even props such as flower petals that were used during festivals.
The arch and concrete are found in many iconic Roman structures. The arch is seen in aqueducts, such as the aqueduct at Segovia, Pont du Gard. The Sanctuary of Fortuna at Palestrina, Italy is a massive temple structure built into the hillside in first century BCE in a series of terraces, exedras, and porticoes. Concrete was used as the primary building material and barrel vaults provide structural support both as a terracing method for the hill and in creating interesting architectural spaces for the sanctuary. Bath structures also make great use out concrete, arches, and a system of vaults and domes. Some of the largest bath structures included vaults or domes that spanned over eighty feet.
Roman aqueducts are another iconic use of the arch. The arches that make up an aqueduct provided support without requiring as much building material that would be needed if the aqueducts were supported by solid walls.