Geolocating Time: Digitisation and Reverse Engineering of a Roman Sundial

Abstract

The sundial of Euporus was discovered in 1878 within the ancient Roman city of Aquileia (Italy), in a quite unusual location at the centre of the city’s horse race track. Studies have tried to demonstrate that the sundial had been made for a more southern location than the one it was found at, although no specific alternative positions have been suggested. This paper showcases both the workflow designed to fully digitise it in 3D and analyses on the use of the artefact undertaken from it. The final 3D reconstruction achieves accuracies of a few millimetres, thus offering the opportunity to analyse small details of its surface and to perform non-trivial measurements. We also propose a mathematical approach to compute the object’s optimal working latitude as well as the gnomon position and orientation. The algorithm is designed as an optimization problem where the sundial’s inscriptions and the Sun positions during daytime are considered to obtain the optimal configuration. The complete 3D model of the object is used to get all the geometrical information needed to validate the results of computations.