Urban planning and ritual action in colonia ulpia traiana (Xanten, Germany): Understanding a non-solar orientation pattern

Abstract

There is increasing evidence to suggest that cosmological factors were applied in the planning and orientation of Roman towns, at least under Augustus. Among others, this is the case of Colonia Augusta Praetoria Salassorum (Aosta) in Italia, Colonia Urbs Iulia Nova Carthago (Cartagena) in Hispania Citerior Tarraconensis, Colonia Copia Claudia Augusta Lugdunum (formerly Colonia Copia Felix Munatia, Lyon) in Gallia Lugdunensis, Colonia Augusta Treverorum (Trier) in Gallia Belgica, and Colonia Claudia Ara Agrippinensium (formerly Ara Ubiorum, Cologne) in Germania Inferior. For the sake of strengthening the sample of cities studied, and identifying orientation patterns from a chronological and astronomical perspective, a number of public structures from Colonia Ulpia Traiana (Xanten) in Germania Inferior were measured. This town was a Roman colony, founded in A.D. 98 by Trajan with a contingent of veteran soldiers and a group of Germanic people. The result was the establishment of a typical Roman settlement with an orthogonal urban grid, whose planning and orientation took cosmological factors into account. In this case, in contrast to the previous examples, we propose that the decumanus maximus was not oriented directly according to the solar arc, but that instead it was possibly linked with other celestial bodies. In addition, the Gallo-Roman temple supposedly dedicated in this town to the Matronae or the Matres was oriented according to the major lunar standstill (“lunistice”). Therefore, this study aims to present the first results regarding the urban orientation of Colonia Ulpia Traiana according to a non-solar pattern, and attemps to provide a preliminary explanation for it from a cultural perspective.