Geodetic Base on the Appian Way

Estremi A e α
Mausoleo di Cecilia Metella, Via Appia Antica, Roma
41°57’07.9”N 12°31’16.1”E (datum WGS84-ETRF2000)

Between 1854 and 1855 Angelo Secchi measured along the Via Appia Antica, from the monument of Cecilia Metella (Rome) to the tower in Frattocchie (Marino), a geodetic base 12043.14 m long.
The geodetic operation along the Appia Antica was born from a double necessity: on the one hand, that of verifying the base measured in 1751 along the same road, always from the mausoleum of Cecilia Metella to the Frattocchie, by the Jesuit Fathers Ruggiero Boscovich and Christopher Maire, a measure whose correctness had been criticized by the French military engineers between 1809 and 1810, on the other, that of having a new measure of reference for the drawing of the cartography of the Papal state and southern Italy.
The geodetic base is the side to which the geodetic triangulation of a region refers (direct and very precise measurement of angles between defined points of the territory) and whose length results from a direct measurement on the ground with an error which must be less than the Mm. With trigonometric formulas It is possible to calculate successively the length of all the other sides taking into account also the curvature of the earth surface.
The starting point of the measurement of the geodetic base (extreme A) was placed by P. Buckets at the center of the Appian Way almost to the height of the cartouche of the mausoleum, far α of the base of P. Boscovich.
To indicate the extreme Boscovichian, the French engineers placed in 1809 a plaque on two metal spikes still visible today and a little lower than the cartouche. The inscription was found in 2011 in the Vatican Museums.
The High CA column. 3.50 m visible on the battlement of the mausoleum in correspondence to the extreme α (upper left in the photo), already existing in the time of buckets, had been used instead for cartographic and geodetic measurements by the astronomer of the Collegio Romano Giacomo Ricchebach, Under the direction of the director of the time, Giuseppe Caladrelli.

Tullio Aebischer, SISFA

Bibliography
A. Secchi: Misura della base trigonometrica eseguita sulla via Appia per ordine del Governo pontificio nel 1854-1855, Roma, 1858, pp. 197; M. Marcelli, I lotto: da piazza Numa Pompilio a via Cecilia Metella in Bullettino della Commissione Archeologica Comunale di Roma, CI, 2000, pp. 334-341; T. Aebischer: Padre Secchi geodeta: 1854/1855 e 1870 in Astronomia, 3, maggio-giugno 2011, pp. 42-49. Atti della Giornata di studio su P. Secchi (II), Grottaferrata (RM), 31 ottobre 2009; G. Filippi, T. Aebischer: Lapide posta dal Governo napoleonico (1809-1814) sul mausoleo di Caecilia Metella per ripristinare il caposaldo occidentale della base geodetica di Maire e Boscovich (1751) in Bollettino dei Monumenti, Musei e Gallerie Pontificie, XXIX, 2011, pp. 175-206; T. Aebischer: Le basi geodetiche storiche della Carta Topografica d’Italia (1875) come monumenti geodetico-cartografici in Atti del convegno nazionale 2011 (Modena, maggio 2011) in Supplemento CD al Bollettino AIC, 143, 2011, pp. 195-208; T. Aebischer: La via Appia Antica parco geodetico. Fonti letterarie e online sulle basi geodetiche di Boscovich e Secchi misurate per la cartografia dello Stato Pontificio e lo studio della forma della Terra (XVII-XXI secc.), Città di Castello (PG), pp. 233, 2014; T. Aebischer, Archeologia geodetica lungo l’Appia Antica (Roma) in S. Adorno, G. Cristina, A. Rotondo, a cura di: VisibileInvisibile: percepire la città tra descrizioni e omissioni, Atti VI Congresso AISU (Catania, 12-14 settembre 2013), collana Collaborazioni - 2, VII. Ritratti di città: città restituite e città interpretate, 2014, pp. 2036-2047; T. Aebischer: Misure geodetiche storiche lungo l’Appia Antica in Ga Gazzetta ambiente, XXIII, nn. 1-2, 2017, pp. 189-192.