- chapter 36: Etruscan town planning and related structures –
and in the carrying out of the Latin ferie (festivals) and the sacrifi ce on Monte Albano.
The unrest of the plebs in the Urbs was not isolated but also included other peoples
in the Latin league. It was actually the hegemony of Rome, subsequently to be clearly
affi rmed, that “caused” the portentum, a sign of danger for the existence of the Latin league
itself, soon to be dismantled (338 bc). From a technical point of view,^29 therefore, how
was the problem to be solved? The overfl ow was collected in underground conduits, thus
regulating the water level in the volcanic basins, and was discharged at lower altitudes
in the countryside surrounding the craters. The tunnels are impressive in their length:
over 1600 meters for Nemi and 1200 for Albano. The correct direction, since there are no
vertical shafts (lumina), could only be obtained by using a groma and a water level.
Although the Buso della Casara is much later, it helps us understand the technical
approach adopted in the creation of these underground conduits. As his point of departure
the author^30 notes that in the aqueduct he studied there were recurrent modules connected
to the stretches that could be dug before calculating anew the direction to follow. The
direction was calculated on the basis of measurements taken in the gallery, an important
element in simplifying (speeding up) the excavation procedures. In short, the working
program might have called for the excavation of a certain number of modules – each
generally 20 feet or approximately 5.9 meters long. A length of this sort allows us to
imagine the use of a rod or a rope marked with the correct distance, at the end of which
the direction was calculated anew. An analysis of the angles measured in the aqueduct
studied by Pesaro tells us that it was always a multiple of 18, as if the measurer had
used an instrument that made it possible for him to effect calculations of this kind, a
sort of alidade divided into 18-degree sections. Examination of the various options has
demonstrated that this is easier to use in a tunnel and is the most trustworthy. The use
of relatively simple equipment coupled with technical-scientifi c knowledge can therefore
be hypothesized. The instrument that comes closest seems to be the dioptra of Hero of
Alexandria,^31 a scientist who probably lived around the middle of the fi rst century ad.
With a groma the scolmatori could be planned on the ground with a simple operation
that allowed the excavation to start from both sides at once and the direction could
be followed, also in underground spaces, with the dioptra.^32 The above-named aspects,
both of a specifi cally religious-cultic and of a technical-operative nature, fi nd their ideal
application in the city of Orvieto, the ancient Velzna.
THE CASE OF ORVIETOConcerning Smyrna, Strabo said: “the regular division of the streets of Smyrna is
noteworthy; the streets are as straight as possible and paved...There is one error, not
a small one, in the work of the engineers, that when they paved the streets they did
not give them underground drainage.”^33 This is not the case with the city of Orvieto
where the subterranean structures bear witness to the a priori planning of the city
layout, involving a whole series of implications of a socio-political nature of considerable
importance, confi rmed by the careful arrangement of the funerary buildings in the city’s
ring necropolis.^34 A glance at the layout of the urban necropoleis (Fig. 36.1), of which
only the stretches of Crocefi sso del Tufo and, in part of Cannicella, respectively on the
northern and southern slopes of the city, are visible today, are indications of how the
social body that held power in archaic Orvieto was capable of regulating the private
sphere, including the funerary sphere.^35