Urban Planning and Ritual Action in Colonia Ulpia Traiana (Xanten, Germany): Understanding a non-Solar Orientation Pattern

There is increasing evidence to suggest that cosmological factors were employed in the planning and

orientation of Roman towns, at least under Augustus. Such is the case, among others, of Colonia Augusta

Praetoria Salassorum (Aosta) in Italia, Colonia Urbs Iulia Nova Carthago (Cartagena) in Hispania Citerior

Tarraconensis, Colonia Copia Claudia Augusta Lugdunum (previous Colonia Copia Felix Munatia, Lyon) in Gallia

Lugdunensis, Colonia Augusta Treverorum (Trier) in Gallia Belgica and Colonia Claudia Ara Agrippinensium

(previous 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 have been 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, the decumanus maximus was not oriented in direct compliance with the solar arc, but we

propose a possible link 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

(“lunastice”). Therefore, this work aims to make known the first results concerning the urban orientation of

Colonia Ulpia Traiana according to a non-solar pattern, and try to provide a preliminary cultural explanation

for it.

Roman Towns. Urban Orientation. Limes Germanicus. Trajan. Matronae. Major Lunar Standstill. Venus.