TRIUMPHAL ARCH. - In Christian architecture it is the great arch that separates the central nave of the church from the presbytery, whether the latter comprises the transept with the apse or the apse alone. In antiquity it often rose on two great columns, but besides this it was always distinguished with special ornaments, either sculptural, as in the basilicas of Syria, or mosaic, as in the great Roman basilicas.
Although the name "triumphal arch" is only of medieval use (and is found especially in the lives of the Popes of the 8th-9th centuries in the Liber Pontificalis, where it is also called arcus maior), we must seek its very origin in the triumphal arches that Roman antiquity was wont to erect for victorious emperors. Just as the ornamental reliefs of these recount the glories of heroes, so too on the triumphal arch of the church the triumph of Christ is willingly represented. On the triumphal arch of Galla Placidia in St. Paul Outside the Walls in Rome we find the majestic bust of Christ on high, surrounded by the four apocalyptic beasts, while from the sides the twenty-four elders offer him their crowns. This apocalyptic triumph of Christ forms the preferred theme in the early Christian triumphal arch. Only, instead of the bust of Christ we sometimes find the lamb or the divine throne. Alongside this representation there often also occurs Christ seated on the globe of the universe among apostles or saints, as for example at Parenzo, in St. Lawrence Outside the Walls, in St. Agatha of the Goths in Rome.
In the Middle Ages the triumph of Christ is represented on the triumphal arch in a manner certainly no less profound and expressive, that is, by the so-called triumphal cross. At the beginning of the curve of the arch the nave was crossed on high by a great beam, on which stood a monumental cross, often accompanied by the Madonna and St. John, a magnificent application of the triumphal hymn of Good Friday Vexilla regis prodeunt... by Venantius Fortunatus. Unfortunately in later times this beautiful expression of the Triumph of Christ was often removed from the churches, and thus with the new forms of a new architecture the ancient triumphal arch also disappeared.