A basilica is a large rectangular hall divided by internal colonnades into a nave and aisles, with the nave carried higher so that windows above the aisle roofs light the interior. It was a secular building: law courts, business, and shelter for the crowd that a forum could not hold in bad weather.
The type solved a problem the temple never addressed, which is how to roof a large interior and light it. Vitruvius describes the proportions; the surviving examples show the range, from the modest basilica at Pompeii to the enormous vaulted Basilica of Maxentius.
When Christianity became a public religion under Constantine it needed buildings for congregations, and the temple was useless for that — it was a house for a statue. The basilica was already a hall for crowds, and it was adopted with its plan essentially intact. The architectural history of the European church begins in a Roman law court.
What the evidence supports
The basilica was a secular building type.
Attested in its Roman uses for law and commerce, and described as such by Vitruvius long before any Christian adoption.
The Christian church took over the plan.
The adoption is visible in the fourth-century foundations at Rome and is not seriously disputed. The reason usually given — that the temple could not house a congregation — follows from what temples were for.
The Basilica of Maxentius used concrete vaulting rather than a timber roof.
Its surviving coffered vaults show the alternative structural solution, and the building's scale was only possible with concrete.
Examples
The evidence level on each answers how we know what the building looked like, not whether it existed.
- Evidence level: Documented
Rome · Begun c. 308 CE
The Basilica of Maxentius and Constantine
Three enormous coffered vaults survive. The colossal statue of Constantine stood in its western apse and was found there in 1486. Three coffered vaults survive standing.
- Evidence level: Documented
Pompeii · Late 2nd century BCE
The basilica at Pompeii
One of the earliest known examples, and evidence that the type was provincial before it was imperial. Excavated to a complete plan.
Primary sources
Vitruvius, On Architecture 5.1
The design and proportions of the basilica, including the one Vitruvius says he built at Fano.
How to read the evidence labels
- Evidence level: Documented
- Supported by a named primary text or by excavated material evidence.
- Evidence level: Probable
- Supported by strong inference that most specialists accept.
- Evidence level: Disputed
- Substantial specialist disagreement exists; competing readings are stated.
- Evidence level: Literary
- Belongs to poetic or mythological construction rather than to history.
- Evidence level: Mythological
- Belongs to shared religious or mythic tradition rather than to any single text.
- Evidence level: Unknown
- The available evidence is insufficient to decide.
These labels describe the status of the evidence, not our confidence in a conclusion. A claim marked Literary is not a claim we doubt; it is a claim about what kind of thing a poem is.