The Tetrastylum (building with 4 pillars in Greek language) was one of the buildings forming the complex of the Arval sanctuary, today located at Magliana Vecchia, at the foot of the sacred grove of the goddess Dia. Unfortunately, it was not identified during the excavation campaigns held by the École française de Rome in 1975 and 1981.
Sallustio Peruzzi, a humanist and architect, son of the other famous architect Baldassarre Peruzzi, wrote in the 16th century that it was allegedly founded by Romulus (“hoc sacellum ordinatum fuit a Romolo“), who in the archaic age would have established the confraternity. It has been identified as a building with a podium (basement) with four columns at the corners and stairs for access. Since there were no walls connecting the columns, the interior would have been visible, showing a simulacrum (statue) and seats for the brothers (triclinia). According to Peruzzi, it was the place intended for the blessing of grain and fields (“ad benedicendum granum et agrum“).
In the recent studies by Broise and Scheid, the function of this type of structure, which had a quadrangular base and corner columns, was investigated: it was to house sacred images and simulacra and to host those taking part in the banquets (epula). Specifically, the Arvals gathered several times in the Tetrastylum of the lucus deae Diae during the second day. After performing the morning rites there, the Arvales would leave it at noon to ascend to the aedes, and would return later to end the festivities, once the sacrifice had been celebrated. The magister would sit there during the morning service, and he and the other fratres would consume the sacrificial banquets in the morning and afternoon there.
The formulas used for this rite in the acta fratrum Arvalium are always very similar: “in tetrastylo consederunt et ex sacrificio epulati sunt” (they sat down in the tetrastylum and banqueted with the animals they sacrificed); “in tetrastylo discumbentes epulati sunt” (reclining in the tetrastylum, they banqueted); “in tetrastylum desciderunt, ibique in triclinio discumbentes ex sacrificio epulati sunt ad magistrum” (they came down into the tetrastylum, and there, leaning on the couches, they banqueted with the animals they sacrificed at the magister’s table); “in cathedris consederunt et epulati sunt” (they sat in chairs and banqueted); “in tetrastylo reversus subsellis consedit” (having returned to the tetrastylum, he sat on the benches); “in tetrastylo subsellis consederunt” (they sat on the benches in the tetrastylum).
A first phase dating back to the Flavian age (2nd century AD) has been recognized, featuring a podium with columns at the corners, which can be compared to the Divorum in the Campus Martius and the aedes Divorum on the Palatine Hill. In a second phase, dated back to the Severan era (3rd century AD), the building was reconstructed with columns on three sides, stairs on the front, and an apse at the back, based on the drawings of Peruzzi and the Dominican father Chacón. Its shape is comparable to summer triclinia protected by a pergola. For the Severan structure, scholars have proposed a comparison with other official religious architectures, including the colonnade of the Ara Maxima of Hercules, which in the 2nd century was precisely a quadrangular area delimited by columns. The banquets following the sacrificial ceremonies of the Ara Maxima were attended by many people, thus transforming it into a place for the manifestation of power. The same can be said of the Tetrastylum, which housed a cycle of excellent sculptures in its apse: the busts and related bases of emperors portrayed as Arval brothers, crowned with wreaths of corn. It has been studied how the statues were found and later got lost: three are still held in two European museums, two in the Louvre Museum in Paris (Antoninus Pius and Lucius Verus) and one at the British Museum in London (Marcus Aurelius). The scholar Evers hypothesizes that this was the gallery of Divi from the 2nd and 3rd centuries, chosen from the statues that decorated the Caesareum at the time it underwent a general renovation in the Severan age.
Reference Bibliography:
J. Scheid, Romulus et ses frères. Le college des Frères Arvales, modèle de culte public dans la des empereurş, EFR 275, Roma 1990
H. Broise, J. Scheid, Tra terra e cielo: la topografia ed il culto del lucus Deae Diae. 2020 in Recherches archéologiques à La Magliana, 3. Un bois sacré du Suburbium romain : topographie générale du site ad Deam Diam. Roma Antica 8. Roma: :École française de Rome; Soprintendenza Speciale Archeologia Belle Arti Paesaggio di Roma
J. Scheid, Gli Arvali e il sito ad Deam Diam, in R. Friggeri, M. Magnani Clementi, C. Caruso, Terme di Diocleziano. Il chiostro piccolo della certosa di Santa Maria degli Angeli, Milano 2014