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Via Appia

GPS survey of the straight segment of Via Appia and computer reconstruction of the Roman centuriation grid

Via Appia, built around 312 BC, is an engineering masterpiece; its most striking feature is the segment between Colle Pardo and Terracina going "straight" for about 61 km. We investigate this segment by GPS techniques: results lead to uncover that the original project of the road was based on a complex interplay between geometry and astronomy.
The project was indeed carried out with the help of a centuriation grid, with all probabilities starting from a node located at the south easternmost point of the grid itself. The road however does not run along the diagonal of the grid: it points to the setting of the star Castor at the time of construction.
Since the Gemini twins were patrons of the Roman army, the project turns out to be a work entertained for both practical and symbolic reasons, during a key moment of the Roman history.

Our GPS survey has been performed between Colle Pardo and Terracina by using a u-blox AEK-4T receiver and the free and open-source software goGPS (Realini 2009). The GPS antenna was positioned on the rooftop of a car with the receiver recording measurements at 1 Hz. The coordinates of more than 5000 points were estimated by applying the double differences method using the GPS permanent station of Latina as base station, every point with an expected accuracy of less than 1 m. The direction of the line interpolating the points was estimated by least-squares adjustment. The resulting azimuth of the whole straight segment of Via Appia is 135° 57' ± 10'

In the following figures the section of Via Appia from Rome to Terracina, together with the roman centuriation grid are shown. The reconstruction of the grid has been based on all the fragments noticed by Cancellieri which we have been able to re-locate from satellite imagery, plus those "discovered" and located on our own.

appia.png    centuriation.png

To better understand the relationship between the road and the centuriation, it is possible to download the Google Earth files (.kml) of the computer reconstruction, also representing the intersection nodes between the road and the grid and the original centuriation traces that are still visible. Finally, very much in the spirit of our Geomatics Laboratory, our computer reconstruction is left "open", meaning that you can freely download the MATLAB script used for this reconstruction; in this way, if further fossil traces are discovered by anyone, they can be easily added to the database, thus improving the whole simulation. References
  • G. Magli, E. Realini, M. Reguzzoni, D. Sampietro. Uncovering a Masterpiece of Roman Engineering: the Project of Via Appia between Colle Pardo and Terracina. Journal of Cultural Heritage.
    Accepted for publication

 G. Magli 
 E. Realini  
 M. Reguzzoni 
 D. Sampietro 

Laboratorio di Geomatica - via Valleggio, 11 - 22100 Como