Reconstruction of the appearance and structural system of Trajan's Bridge

Trajan's Bridge, built by Romans over the Danube River in the first years of the II century, was the first kilometer-long bridge ever built. It was a marvel of Roman engineering, especially taking into account challenging site conditions, available resources and record time for construction. The bridge's still-standing columns are witnesses to its masterful construction. The bridge was later intentionally destroyed by Romans, and several researchers in the past studied the bridge and attempted to reconstruct its appearance and structural system. However, the dearth of information generally associated with destroyed ancient structures makes their reconstruction extremely challenging. In the case of Trajan's Bridge, the only confirmed representation of the structure is on Trajan's Column, found just north of the Roman Forum. Nevertheless, several studies performed in the past proposed a structure different from the one shown in the Column. Most of these studies are not based on detailed structural analysis, and thus some of them do not seem to be credible from the engineering point of view. The aim of this paper was to reconstruct the structural system and appearance of Trajan's Bridge using structural analysis, and to determine to what extent the representation of the structure on Trajan's Column could be accurate. This is successfully performed by determining the number of degrees of freedom associated with the structure and by analyzing the materials, stresses, and the bridge construction technique.