Arco di Giano
Via del Velabro
early 4C AD
Today this building is identified as the Arcus Constantini, which Constantine's regional catalogues mention for Regio IX. It is a tetrapylon with four arched, and two passages which intersect in the form of a cross. This type of structure was known since the time of Augustus (Cavaillon), but equal importance was not given to all four sides until the Arch of Galerius was built in Thessaloniki in the period of the tetrarchs. It was in that period that Constantine then assumed the dictatorship. Like the earlier examples, Janus Quadrifrons was probably topped by a superstructure, but this was removed in 1830 along with the medieval tower which the Frangipane family had placed on top.
Janus is the Roman designation for this structural type, and is at the same time the name of the god of routes and beginnings. His shrine in the Forum Romanum consists of two passages which were opened in wartime and closed in peacetime. Constantine chose the point where two old routes intersected as the site for this structure. One of them ran from the venerable Forum Boarium to the Velabrum depression and thus to the political Forum Romanum. The Cloaca Maxima also followed this route. The second route, proceeding from north to south, was the trade route to which Rome owes its origin.
There are two characteristic design principles, both of them in the Roman late-classical spirit: the building is subdivided by niches with shell-shaped vaults and, between the niches, by small columns (now lost) supported on corbels. These elements are placed so regularly and so close together that the impression of a glittering carpet is aroused, very much at variance with the weighty, cube-shaped mass of the building. A feature of similarly atectonic, late-classical design is the horizontal strips which line Janus Quadrifrons on all sides, even in the passages, thus degrading him to a mere bearer of linear decoration.
Stefan Grundmann, The Architecture of Rome (Stuttgart: Editions Axel Menges, 1998), p. 64.
Kalervo Koskimies 1997
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