"And among those gods which ought to be placated in order to avert evil influences from ourselves or our harvests are reckoned Auruncus [from averrunco, "to avert") and Robigus."
Aulus Gellius, Attic Nights (V.12.14)
Instituted by Numa Pompilius, the Robigalia, an ancient agricultural festival celebrated in honor of Robigo (or Robigus, the gender was uncertain), the goddess of blight, red rust, or mildew, was celebrated on April 25, when the crops were most vulnerable to disease (Pliny, XVIII.285; also Varro, On Agriculture, I.1.6; On the Latin Language, VI.16). In his poem for that day, Ovid relates that he, himself, happened to meet the priest as he and his followers, all dressed in white, were on their way to the sacred grove to offer sacrifice. Joining the procession, he relates how the flamen Quirenalis carried with him the entrails of both a dog and a sheep. Incense, wine, and entrails were thrown on the fire and a prayer offered. "Scaly Robigo, god of rust, spare Ceres' grain; let silky blades quiver on the soil's skin. Let growing crops be nourished by a friendly sky and stars, until they ripen for the scythe...Spare us, I pray keep scabrous hands from the harvest. Harm no crops. The power to harm is enough" (Fasti, IV.911ff).
A similar prayer is given by Cato in his treatise on agriculture, "Father Mars, I pray and beseech thee that thou be gracious and merciful to me, my house, and my household...and that thou permit my harvests, my grain, my vineyards, and my plantations to flourish and to come to good issue, preserve in health my shepherds and my flocks, and give good health and strength to me, my house, and my household" (De Agricultura, CXLI). Here, like Robigo, the god is evoked to avert harm because he has the capacity to create it. The priest of Quirinus, a less martial aspect of Mars, also beseeches the god not to damage the crops. That there was an agricultural affinity between these deities can be seen in a passage from Tertullian, who records that "Numa Pompilius instituted games to Mars and Robigo (for they have also invented a goddess of rust)" (De Spectaculis, V).
When Ovid asked the priest why a dog had been sacrificed, he was told that related to the rising of Sirius, the Dog Star, which coincided with the heat of summer, causing the crops to ripen prematurely. This association is probably incorrect (Sirius actually sets then) and it may be that neither Ovid nor the priest really knew the reason. Columella does speak of a young dog being sacrificed to appease the goddess (De Re Rustica, X342ff; also Pliny, XVIII.15), and a fragment from Festus indicates that red dogs were sacrificed to appease the Dog Star that the corn might ripen. It may be, too, that the color of the dogs and the ripening corn (or the red rust) were sympathetically related.
The detail above is from the Fasti Praenestini, which is in the Palazzo Massimo Alle Terme (Rome), and pertains to April 24-26. April 25 (VII Kal. Mai.) marks the date of the Robigalia. As can be read in the calendar, the grove of the deity was at the fifth milestone on the Via Claudia: Feriae Robigo Via Claudia ad milliarium V ne robigo frumentis noceat....
References: Ovid: Fasti (2000) translated by A. J. Boyle and R. D. Woodard (Penguin Classics); Cato: De Agricultura (1934) translated by W. D. Hooper and H. B. Ash; Varro: On the Latin Language (1938) translated by Roland G. Kent (Loeb Classical Library); Varro: On Agriculture (1935) translated by William Davis Hooper (Loeb Classical Library). An English translation of De Verborum Sgnificatu by Sextus Pompeius Festus has not yet been translated into English.
