Colosseum: Underground

History of the Colosseum’s Underground

The Colosseum’s underground levels (the “subterraneans”) rank among the most fascinating and technically sophisticated aspects of ancient Rome. These spaces, conceived to support the spectacular functioning of the arena, went through various developmental phases over the centuries, mirroring the functional and symbolic transformations that affected the Colosseum. Below is an overview of the main historical periods that shaped the evolution of these underground areas.

Flavian Origins: Early Design and Initial Functions

Context and Construction

Construction of the Flavian Amphitheater began between AD 70 and 71 under Emperor Vespasian, and it was partially completed in AD 80 during the reign of Titus. From the earliest planning stages, the Flavians envisioned a multipurpose amphitheater: in addition to the massive arena intended for shows, service spaces were to be built underneath. Although the underground at that time did not yet have the complex layout it would later assume, there were already initial corridors and passages designed for the swift transport of animals, gladiators, and stage props.

The Arena and Its Scenic Floor

In the Flavian era, the arena floor consisted of a mixed layout: a perimeter in masonry and a central area supported by wooden beams, covered with a layer of sand regularly renewed. The possibility of flooding the arena for naval spectacles (naumachiae) depended on a floor system that allowed rapid dismantling and reconfiguration of the surface. Although in this first phase the subterranean solutions were primarily functional, they laid the groundwork for the subsequent development of the hypogeum.

Under Domitian: Expansion and Structuring of Underground Spaces

Structure and Organization

During the reign of Domitian (AD 81–96), the Amphitheater experienced a major expansion phase. At that time, the underground was more systematically and solidly built in masonry, resulting in a complex, articulated hypogeum. Designed to enable an organized flow of workers, gladiators, and animals, this system ensured rapid changes of the scenic setups.

Operational Functions

The subterranean spaces constructed under Domitian served multiple operational purposes:

• Access and Circulation: A central corridor running along the arena’s main axis, flanked by numerous side passages, allowed simultaneous entry from different points.
• Storage of Materials and Stage Props: These areas facilitated storing and swiftly moving scenic elements, including clean or used sand as well as the hoisting and handling apparatuses.
• Support for Shows: The layout of the underground was geared toward rapid set changes, enabling quick appearances and disappearances of gladiators and animals, thus enhancing the shows’ spectacle.

Transformations in Late Antiquity and the Middle Ages

Functional Changes and New Meanings

With the decline of pagan spectacles and the rise of Christianity, the original function of the underground underwent profound changes. In Late Antiquity and the following centuries, fewer gladiatorial events led to a gradual abandonment of the underground’s purely operational uses.

Religious Interpretation and Devotional Use

In the Middle Ages, the underground areas of the Colosseum took on symbolic and religious significance. Many medieval sources link these spaces to the memory of martyrs, making them part of local devotional practices. For instance, accounts mention “sacred soil” soaked with martyrs’ blood that was collected and employed in religious rites, endowing the site with the status of a relic and bearing witness to the Christian persecution.

Archaeological Rediscovery and New Interpretations in Modern Times

Rise of Systematic Studies

Starting in the 19th century, as archaeological excavations intensified and scientific methods developed, the Colosseum’s underground began to be studied comprehensively. These investigations have reconstructed in detail the intricate internal organization of the hypogeum, highlighting the remarkable engineering precision adopted by the Romans.

Documentation and Critical Reassessment

In the 20th and 21st centuries, contributions from archaeological research institutes and cooperation with the Archaeological Superintendency of Rome have led to numerous studies of the underground. These efforts clarified the original functions of the spaces, illustrating their evolving uses over time and demonstrating how the Romans incorporated advanced engineering and construction methods for that era. Modern reassessments have further emphasized that the hypogeum was not only a logistical support for spectacles, but also a symbolic element reflecting Rome’s cultural and religious complexity.

Description and Structure of the Colosseum’s Underground

Known as the “hypogeum,” the Colosseum’s underground forms one of the most complex and innovative architectural systems of Roman engineering. Designed to support the amphitheater’s “stage machine,” it streamlined the quick movement of gladiators, exotic animals, and scenic elements. Over the centuries, this internal layout — a network of corridors, service areas, and dedicated access points — underwent multiple modifications, while still retaining original structural features that showcase the Romans’ advanced design capabilities.

Corridor Architecture and Spatial Organization

The corridors forming the backbone of the hypogeum were built using the typical Roman construction methods of the period. Barrel vaults in masonry, made with opus reticulatum or opus incertum, ensured the building’s stability and divided the extensive underground zone into functional, modular sections.
These long, narrow corridors extend along the arena’s main axis, branching into numerous lateral passageways for rapidly transporting scenic elements. Their layout, characterized by load-bearing walls and openings for lighting (originally provided by torches and oil lamps), also facilitated water drainage, a crucial aspect in a space susceptible to periodic flooding.

Functional Segmentation of Spaces

The Colosseum’s underground can be divided into various areas, each serving a specific purpose:

Central Zone and Main Corridor

The central corridor, running along the amphitheater’s major axis, served as an organizational hub. Numerous passages branched out from this area, connecting the arena with storage and preparation rooms. Access to this corridor was critical for coordinating operators handling stage props, equipment, and the animals used during the shows.

Service and Storage Areas

Along the side corridors were rooms used for storing and preparing stage elements. Such areas included equipment storerooms, holding zones for gladiators and animals, and small workshops for quickly assembling and dismantling stage setups. Their modular layout ensured efficient logistics, making it possible to refresh the arena “stage” in minimal time.

Entrances and External Connections

The underground complex features multiple points of access, strategically designed to separate operators’ movements from the public’s. Among these is the famous Porta Libitinaria, historically tied to the ritual removal of fallen gladiators’ bodies. Other entrances, scattered along the corridors, provided direct links to the cavea (seating area) and to the Ludus Magnus complex (the gladiator barracks). These access routes were essential for rotating participants quickly and coordinating the diverse functions carried out within the hypogeum.

Materials and Construction Techniques

The underground areas were built using high-quality materials and advanced techniques for the time. The use of tuff blocks, travertine, and bricks, coupled with the opus caementicium method, resulted in sturdy, long-lasting load-bearing walls. The original floor, often featuring opus spicatum, exemplifies Roman construction methods, though over the centuries modifications and reinforcement works have layered the structure in different historical phases.

Historical Evolution and Later Interventions

The Colosseum’s underground has not remained static. Throughout the post-Flavian era and Late Antiquity, several reinforcements and adaptations were introduced to match new functional or devotional requirements.
In Late Antiquity and the medieval period, with the gradual discontinuation of large-scale shows, parts of the underground were abandoned, then repurposed for other uses until eventually being filled in. Only with modern archaeological investigations, begun in the 1990s, was it possible to document the complexity of the hypogeum thoroughly, identifying modifications made during the Trajanic, Severan, and Late Antique periods.

Visiting the Colosseum’s Underground

Exploring the Colosseum’s underground offers a unique glimpse into the engineering and operational organization behind the ancient amphitheater. This guided tour invites visitors to discover the concealed spaces that once served as the “backstage” for gladiatorial shows, animal hunts, and naval spectacles.

The Tour Route

The underground tour typically begins near the main entrance, located on the north side of the amphitheater by the so-called “Stern spur.” From here, visitors are led down the central corridor, which runs along the arena’s main axis. This long passage, recognizable by barrel vaulting and ancient masonry in tuff, travertine, and bricks, formed the backbone of the amphitheater’s “stage machine.”

Along the way, your guide will describe the various areas and their original functions:

• Main Corridor and Lateral Galleries: These passages linked the arena to service areas where scenery was assembled and the movement of gladiators, animals, and equipment was coordinated.
• Specific Entrances: Among these is the historic Porta Libitinaria, used for transporting fallen gladiators’ bodies. Other entrances allowed direct access to the cavea and to the Ludus Magnus complex, the gladiator barracks.

What You Will See

During a guided visit to the underground, travelers can observe and understand various structural and functional elements:

• Original Vaults and Walls: The ancient corridors, built according to Roman engineering techniques, still display evidence of opus reticulatum and opus incertum, attesting to the project’s solidity and modular design.
• Water Drainage System: You will learn how canals dating from ancient times allowed water to be rapidly drained — crucial for the naumachiae, when the arena was flooded for naval shows.
• Service Areas: Spaces used to store and prepare stage apparatus, as well as holding pens for gladiators and animals, are partly visible thanks to recent archaeological recovery efforts.
• Functional Devices: Traces of lifting mechanisms (hoists and movable platforms) and openings once used to quickly transfer props and performers highlight the amphitheater’s intricate operational design.

Tickets and Tours

Access to the Colosseum’s underground is restricted to guided tours, essential for safeguarding the monument and preserving its historic areas. Tickets for the tour can be purchased online through the official website of the Parco Archeologico del Colosseo or via authorized agencies.
Several options are available:

• Standard Guided Tour: Offers a comprehensive route through the underground, featuring detailed explanations from specialized guides.
• Combined Tour: Includes underground access as well as other noteworthy areas of the Colosseum, providing an integrated view of the entire complex.
• Private Visits: Provide a tailored experience, with flexible routes and opportunities to delve more deeply into specific aspects of the organization and history of the hypogeum.

The experience is further enhanced by audio-guide devices, offering detailed commentary and enabling visitors to fully appreciate the historical and architectural complexity of the underground spaces.