The main streets of the city, apart from the Via Aemilia which coincided with the decumanus maximus, formed a regular and composite grid, with some differences due to the evolution of the urban layout over time.
They were laid out starting from the decumanus maximus, therefore parallel and perpendicular to the via Aemilia; moreover, they were harmonious with the axes of the centuriation (oriented about 21 degrees to the north-east), which neatly divided the flat territory administered by Claterna thanks to a network of roads and canals organized in square meshes of about 710 m side. In this way, the urban centre was perfectly integrated in the territory and directly connected to the countryside, playing the role of service centre for the wide surrounding area.
Among the currently known streets, some, located in the south-eastern quarter closest to the Quaderna stream, had an ‘astronomical’ orientation, i.e. exactly north-south, generally preferred in the most ancient times; according to some scholars, this type of alignment would indicate a greater antiquity of this portion of the city.
Surface researches carried out in the 1980s and 1990s on the whole city and part of the suburbs, together with aerial photographs, made it possible to identify the orientation and extension of the main road axes; some targeted archaeological tests brought to light large portions of them, clarifying their construction characteristics. The roadbeds were formed by the filling in of small and medium-sized gravels, while the transit surfaces were paved with medium to large-sized cobblestones, well connected to each other.
As can be seen, in contrast to other cities, ‘trachytic basalt’, the large irregular polygonal elements of limestone or volcanic rock that were quarried and processed specifically for road paving, were not used in Claterna. At some points in the urban road network, however, comparable devices were used; for example, at the junction of the cardo and decumanus maximus, west of the forum, a more robust and elegant paving was adopted, using larger than usual flakes and pebbles and laid with particular care.
At this central crossroads numerous ‘cart tracks’ were evident, furrows left by the intense passage of carts; their direction seems to attest also in Claterna a practice already archaeologically documented in other Roman cities: in the city centre, corresponding to the forensic area, vehicular traffic was forbidden. This is a very up-to-date rule, which shows that even two thousand years ago the problem of traffic and its management was a constant part of everyday life.