The Uaratio and Its Possible Use in Roman Urban Planning to Obtain Astronomical Orientations

Abstract

Several works have tried either to demonstrate or reject the notion that the orientation of the main axis of a Roman city was deliberate since its choice might add an extra sacred dimension to the entire urban space Magli 2008). There exist ancient texts that support the hypothesis of the existence of astronomical orientations, such as those of Frontinus (De Agrimmensura, 27) or Hyginus Gromaticus (Constitutio,I). In the case that these precepts were fulfilled: how to achieve it? Besides the astronomical hypothesis, some scholars have pointed to the use of a geometrical technique: the uaratio (Orfila et al. 2014). By this, the short sides of a regular triangle that are in ratios of integer numbers (for example 1:2, 2:3) are laid along the cardinal axes. In this work we present a comparison of the orientation of 81 Roman towns in the Iberian Peninsula, measured in situ, with uaratio angles with aspect ratios up to 12:12. By this exercise we want to discern whether the orientations were astronomical, purely geometrical, or if geometry could have fostered astronomical aims by using selected and well-known angles to trace lines that fitted the desired astronomical purposes. It is then, an attempt to shed more light to the issue of the orientation of Roman towns by combining two hypotheses that, in contrast to what it might seem, could be complementary but not contrary.

Between Land and Sky—A Study of the Orientation of Roman Centuriations in Italy

“…At first glance, regarding the orientation patterns displayed in the different curvigrams, we can identify that 70% of the declinations coincide with values for the rising sun. In addition, some maxima may correspond to the practice of astronomical observations or the application of simple geometrical techniques such as the varatio-previously studied for Roman towns in Hispania [25,41]-together with more dispersed data that could be explained by diverse environmental restrictions of the terrain where centuriations were located.…”

“…Finally, the use of geometry should not be dismissed either, as suggested by the maxima around δ ≈ +26 • and δ ≈ +17 • in the centuriations' curvigram of declination (Figure 3), which are compatible with the use of the Pythagorean triangles 3:4:5 and 5:12:13, respectively, for null altitudes of the horizon and medium Italian latitudes. The role of geometry in the layout of land has been explored in several studies on Roman land and urban design across the Empire, with both practical and symbolic intentionality [14,25,41,47] and, in addition to hypothetical direct observations of particular astronomical phenomena (such as sunrises on special dates), astronomy was also required for the implementation of particular geometric relations to the cardinal axes by using a gnomon (see, e.g., [25]).…”

“…In Italy specifically, several Roman towns were studied [20,21], including Rome itself [22], together with the masterpiece of Roman engineering that is the Via Appia [23,24], which is a clear example of the integration of astronomical phenomena in Roman land organization. In addition, the implementation of a particular geometrical technique (the varatio) for the orientation of the main axes was explored in Roman towns in the Iberian Peninsula, leading to the conclusion that geometry might have also been used with possibly astronomical purposes [25]. These works prompted us to study the case of the centuriations in a similar way.…”

The Geometry in the Urban Layout of the Roman Como and Verona: The Same Solution to Different Problems

“…Besides the study of varato concerning the Hadrian's Wall and the Wetterau Limes [9], we can fnd the varato considered for the orientaton of the Roman towns in Spain [13]. In [14], the approach of [13] is considered with a specifc aim. The authors of [13], that have studied the orientaton of 81 Roman towns in the Iberian Peninsula having varato angles with aspect ratos up to 12:12, "want to discern whether the orientatons were astronomical, purely geometrical, or if geometry could have fostered astronomical aims by using selected and well-known angles to trace lines that ftted the desired astronomical purposes."…”

“…Of course, also for the Roman towns in Italy, the study of their varato could be an interestng research. The reason of the research could be the same as for [14]. In the case we have a town that seems oriented, for instance, to the sunrise on solstces, we could ask ourselves if this town was subjected to a procedure of varato too.…”