Roman Imperial Architecture

Colosseum, Rome, 75-80 CE

Built under Emperor Vespasian (c. 70–80 CE)

The Colosseum was not just a marvel of Roman engineering—it was also a powerful tool of imperial propaganda. Commissioned by Emperor Vespasian, founder of the Flavian dynasty, the amphitheater was built on the site of Nero’s former private palace. By returning this land to the public and constructing a grand arena for entertainment, Vespasian sent a clear political message:

• The new emperor serves the people, not personal luxury.

The Colosseum symbolized the strength, generosity, and authority of the Flavians. Spectacles held there—gladiator games, animal hunts, and mock naval battles—reinforced the image of Rome’s military power, social order, and imperial benevolence.

Often considered the sum of Roman architectural achievement, the Colosseum is a Roman invention: an amphitheater, created by combining two facing theaters to enclose an oval arena. It remains the largest amphitheater in Rome, with a seating capacity of approximately 50,000 spectators.

Exterior Features

• Constructed primarily of travertine limestone.

• The facade consists of three main stories, each with 80 arched openings on the ground level to allow smooth crowd circulation.

• Each level is flanked by engaged columns in the following order:

  • Doric on the first level

  • Ionic on the second

  • Corinthian on the third

• This decorative progression of classical orders reflects Roman architectural hierarchy and design sophistication.

• Above the third story was a fourth level with small rectangular windows and sockets for the velarium—a massive retractable awning that provided shade to the spectators.

Interior of the Colosseum

Interior Features

• The arena floor covered a vast substructure of vaulted corridors, cages, and holding areas—used for housing animals, gladiators, and equipment.

• This basement area (hypogeum) was a marvel of Roman engineering, allowing dramatic stagecraft such as elevators and trap doors.

• The system of circulation was clear and efficient, enabling tens of thousands to enter and exit rapidly—an early example of crowd control design.

• The use of concrete allowed for the creation of these vast vaulted spaces and stands, revolutionizing Roman architecture. This innovation also made possible other monumental works like the Pantheon.

Pantheon, Rome, 118-125 CE

Commissioned during the reign of Emperor Hadrian

“Pantheon” means “temple of all gods.”

One of the best-preserved monuments of ancient Rome, the Pantheon is a remarkable achievement in both engineering and architectural design. It represents a major shift from the Greek focus on solid form to the Roman focus on space and volume—a structure that evokes awe not through its mass, but through its interior spatial experience.

Exterior

• The front features a traditional Greek temple façade with:

• A portico of Corinthian columns supporting a plain entablature and pediment (which originally held no sculpture).

• Behind this classical front rises a large circular drum topped by a massive dome, signaling a surprising transition from traditional form to innovative Roman design.

• Originally, the Pantheon was approached through a forecourt, now lost, which would have enhanced the dramatic effect of the sudden shift from exterior simplicity to interior grandeur.

Interior, Pantheon

The interior is based on perfect geometric harmony, formed by two intersecting circles:

• The diameter of the dome is equal to the height from the floor to the oculus—144 feet—creating a perfect sphere.

The space is divided into three vertical zones:

1. Ground floor with niches and recesses

2. Intermediate cornice

3. Hemispherical dome

• The oculus (a 29-foot-wide circular opening at the top of the dome) is the only source of light, creating dramatic illumination that shifts throughout the day.

• The vast, unobstructed central space (no columns interrupting the core) represents the first time in architectural history that such open interior volume was fully realized.

• The design emphasizes architecture of space, not mass—unlike Greek architecture, which focused on solid, balanced structures.

Detail - rendered drawing

Oculus of the Pantheon: Fascinating Facts

• Only Source of Light

  • The oculus, which is 29 feet (8.8 meters) in diameter, is the only source of natural light in the Pantheon. It creates a dramatic spotlight effect that shifts throughout the day, symbolically connecting the temple to the heavens.

• Symbolic Eye to the Sky

  • “Oculus” means “eye” in Latin. In Roman thought, it symbolized the eye of the gods or a connection between the temple and the divine. It lets the heavens “watch over” the worshippers below.

• Uncovered and Open to the Elements

  • The oculus is completely open to the sky, meaning rain can and does fall inside. However, the floor of the Pantheon is slightly sloped and contains drainage holes to carry water away efficiently.

• Structural Genius

  • The oculus is not just decorative—it's structural. Removing the center of the dome reduces the weight at its most critical point. This lightens the load and helps prevent collapse, showcasing Roman engineering brilliance.

• Perfect Geometry

  • The oculus completes the dome’s spherical shape. The interior forms a perfect hemisphere—the same height as the diameter (144 feet)—with the oculus at the apex, reinforcing the harmony of the space.

• Astronomical Significance

  • Some scholars believe the oculus served an astronomical purpose, aligning light with specific spots in the Pantheon on important days, such as the emperor’s birthday or equinoxes—highlighting the cosmic symbolism of Roman imperial rule.

• Survived for Nearly 2,000 Years

  • The Pantheon’s oculus has remained open and functional for almost two millennia, surviving weather, earthquakes, and time—testament to the durability of Roman concrete and design.

Plan of the Pantheon

The Pantheon’s plan combines a traditional Greek-style portico with a large circular rotunda, creating a unique blend of old and new. Inside, the space is based on perfect geometry—the diameter of the dome is equal to the height from the floor to the oculus (144 feet), forming an invisible sphere. The interior is laid out with seven large niches around the circular wall and eight massive piers supporting the dome. There are no columns in the center, allowing for a vast, open space. The coffered dome reduces weight, and the oculus at the top provides natural light. The floor is slightly sloped to let rainwater drain through hidden channels. This design reflects Roman values of order, harmony, and engineering innovation.

Interesting facts:

The Pantheon also serves as a tomb, housing the remains of:

• Raphael, the Renaissance painter

• Italian kings Victor Emmanuel II and Umberto I

• Queen Margherita of Savoy

Inspired Countless Buildings Worldwide

The Pantheon has influenced the design of many important structures, including:

• The U.S. Capitol Building

• The Pantheon in Paris

• Numerous Renaissance churches and Neoclassical government buildings