The term “basilica” is used to refer to a specific architectural style, and also in an ecclesiastical sense. A religious basilica may or may not retain the traditional architectural form. The term has come to be used to designate buildings of extreme historical or religious importance by the Roman Catholic Church. A structure designated as a religious basilica is entitled to certain privileges, and there are a number of greater and lesser basilicas scattered across the world.
In architectural terms, a basilica is a large building which has a usually rectangular central area called a nave. Columns line either side of the nave, creating a feature known as a colonnade. An apse, a vaulted recess, was usually located at one end of the basilica. Originally, a basilica was an administrative building. Indoor markets could be held in the colonnade, and large numbers of people could gather in the nave to deal with various administrative tasks. Major authorities would be located in the apse, which could be used for formal meetings and hearings. The oldest such building appears to have been built in 184 BCE, by Cato.
As the Christian church began to expand, the need for large buildings in which to worship arose. Christians wanted to distance themselves from pagan outdoor ceremonies, and began to build churches, structures in which religious worship could take place. The form of a basilica lent itself well to religious building, as the altar could be located in the apse and worshipers could be seated in the nave and colonnade. The basilica design began to dominate religious architecture.
Ultimately, the term began to be used more generally by the Roman Catholic Church to refer to an integral religious building. A church which is classified as a basilica tends to be imposing, beautiful, and important. The most important basilicas are designated for the Pope's use, and are occupied for the celebration of important masses. Even lesser basilicas still have the right to important religious privileges, such as special ceremonial items to be carried in procession and a formal cape worn by the officiant at major religious holidays.
The most important religious basilica is generally considered to be St. Peter's, in Vatican City. It is used by the Pope on important locations, and is also the largest religious building in the world. The prominent building is famous among Roman Catholics all over the world, and also serves as the burial site for many well known religious figures in the Catholic Church. The interior of the basilica is lavishly decorated, and it is a popular destination for tourists.