They were eventually used by the Christians as sites for reunions and prayer and the word has therefore gained a duplicate meaning.
The layout of the basilicas was to have a large central isle flanked by two isles, one to either side of the main one. The central isle would also be taller than the sides so that windows in the top section might let light into the building.
An apse at the end, possibly raised from the floor level, would provide a focal point to public reunions for example with seating for judges or other high ranking persons. The Christians made use of the apse for the altar. The apse itself was set off from the rest of the building (the congregation) by way of a large triumphal arch.
The walls would be supported by rows of columns into which the weight of the walls would be channelled by way of arches. The use of columns and arches enabled the overall floor area to be very significant, especially if arch and vaulting methods were employed as in the basilica of Maxentius in the Forum.
The roof would be held by wooden trusses and covered in terra-cotta tiles. The width of the central isle would be therefore limited by the possibility of building sufficiently wide roofs without the danger of them caving in which in great degree would be limited by the length of the wooden beams available. This limitation was obviated in buildings such as the Colosseum where large areas were spanned with the use of lightweight materials such as sails, but this was clearly not a viable solution for permanent roofs in buildings such as the basilica.
Basilicas of Rome
Given the strong focus on public life in ancient Rome it would be unnusual for any city of the empire to be without its own basilica in which to run state bureaucracy and business.
Famous basilicas the remains of which may still be visited include the basilica Iulia, Ulpia and of Maxentius in the Roman Forum.
Ecclesiastical basilicas which still give a strong sense of the structure and architecture include:
the basilica of Saint Paul outside the walls of Rome (the architecture dates as far back as Emperor Constantine but it was actually rebuilt after a devastating fire in the 19th century)
The basilica of Santa Maria Maggiore
the basilica’s on the Aventine hill such as Santa Sabina
Possibly the most famous is the Basilica of St. Peter but the actual structure has little in common with ancient Roman basilicas as architects of the renaissance and baroque periods changed the focal point of the building towards the centre, added domes and made strong use of references to classical buildings such as the Pantheon.