The eruption of Mt. Vesuvius destroyed the opulent vacation destinations of Roman elites in August 79 C.E.—almost exactly nine years after Roman troops destroyed the Temple in Jerusalem. In the July/August 2010 issue of BAR, Hershel Shanks asks whether the ancients drew a link between these two events—perhaps understanding the volcanic eruption as God’s revenge on the Romans for the destruction of his Temple. In his article “The Destruction of Pompeii—God’s Revenge?”  Shanks also examines some of the evidence for a Jewish presence at Pompeii.
One of the most intriguing, though by no means conclusive, clues comes from ceramic jars labeled garum castum, or “pure” garum. Garum, was a sauce—a popular Roman delicacy—that was made from various types of fish and marine life. According to the dietary laws of kashrut, Jews are not supposed to eat fish without scales (including shellfish). The ancient Roman naturalist and author Pliny the Elder, who perished in the eruption of Mt. Vesuvius, suggested that there was a special type of garum made at Pompeii for Jews, which would presumably be considered kosher. Was this garum castum the kosher fish sauce?
Some scholars have argued that this “pure” garum may not have been intended for Jews at all, but rather for the followers of other Greco-Roman mystery religions that observed dietary restrictions or purity laws. In this letter (see below) to BAR editor Hershel Shanks, Classics professor Robert I. Curtis of the University of Georgia clarifies and expands on his own interpretation of the garum jars and what they might suggest about the Jewish population at Pompeii.
Professor Curtis’s letter to Hershel Shanks about garum castum follows below.
Letter from Robert Curtis to Hershel Shanks:
Garum Castum and the Jews
by Robert Curtis 
I read the discussion by Hannah Cotton on the garum inscription (titulus pictus), recorded as No. 826 in Masada II (pp. 166–67), in which, citing me and Frey, she concludes that “it seems that the garum castum was not, after all, intended for Jews” (p. 166). While not going into detail (I can if you wish), she has apparently misinterpreted what I had written. Perhaps I wasn’t very clear. In any case, seven years later, she seems to have changed her mind. In her Journal of Roman Archaeology article (9: 223–38) she concludes that “these labels might not [my emphasis] have been specifically for Jews, but for people who practiced abstinence in general” (p. 237). This statement is in line with what I wrote in 1991. She goes on two paragraphs later in the same article to state, “And if we are right to assume [my emphasis] that the allec was kosher, then it is very plausible that Masada II, no. 826 contained kosher garum.” As I read her most recent pronouncement, her view now coincides with mine and yours as I read them in the abstract that you sent to me. A more recent article on this amphora will be of interest to you, though it doesn’t add anything to the question at hand: Piotr Berdowski, “Garum of Herod the Great (a Latin-Greek Inscription on the Amphora from Masada,” Analecta Archaeologica Ressoviensia 1(2006): 239–57.
Pliny’s reference (HN 31.44) to a special garum makes two points: (1) the garum was made from fish without scales (quod fit piscibus squama carentibus); and (2) the garum was special to two specific groups: Jews (or, sacris Iudaeis) and those devoted to sex abstinence (or, castimoniarum superstitioni). Pliny is, of course, in error in suggesting that Jews would eat fish without scales in any form. So, is he wrong to include Jews as the target group for garum made from fish without scales or does he err when he says that the special garum for Jews was made from fish without scales? If the former, then there is nothing to discuss, since this garum would not be special to Jews, indeed, just the opposite. If the latter, and everyone makes this assumption, then the special garum was actually a fish sauce made of fish with scales and so explicitly permitted to Jews. Working under the latter assumption, then, the question at hand is whether this special garum that Pliny describes is the same as the product held in vessels found in Pompeii that possessed labels indicating their contents as either garum castum or allec casta? In other words were they kosher fish sauces? Also, could they have been destined for a clientele other than Jews?
Vessels containing garum castum and allec casta found in Pompeii bore a label that identified not just garum but a special garum, one that was castum (“pure”). Purity here is not a reference to an unadulterated or unmixed product (many garums did contain more than one fish or additive or, if not, were labeled with the name of the specific fish used) but one that is morally or spiritually pure. As such, it no doubt was intended for a particular clientele and was labeled so for easy and unambiguous identification. Evidence for a Jewish population in Pompeii seems to me to be conclusive, although it is not possible to say how large that presence was. This also holds for the presence of cult followers of various mystery religions, including those that practiced sex abstinence and food restrictions, such as Isis, Apis, Magna Mater, and Attis. These come immediately to mind, since Pliny’s use of superstitioni strongly implies a cult outside of or on the fringes of Graeco-Roman religion. As with the Jewish population, however, we do not know how plentiful these groups were in Campania. All we can say is that Jews and worshippers of Isis, Apis, Magna Mater, and Attis resided contemporaneously in Campanian towns in the first century A. D. The ancient sources on the cult practices of these pagan mystery cults are not very forthcoming and the information that we do have is primarily from authors hostile to them. So, 100% certainty on matters regarding fasting and abstinence is impossible.
Ancient fasting and abstinence took on a variety of forms. In general, they fell into two broad groups: abstinence from all food for a fixed period and abstinence from a particular food or foods either all of the time or for a fixed period. The first group included especially Christian ascetics and does not concern us here. The second group would include philosophers and medical writers, such as Hippocrates, Galen, etc., whose “lifetime” restrictions on certain foods were made not in the context of religion but of health (especially dietetics). The Jewish attitude toward fish without scales, on the other hand, is also clearly of the second group (i.e., abstinence from a specific food all the time) but is religiously motivated. I am not aware that followers of Isis, Magna Mater, etc. exercised restrictions of this kind. They did, however, have abstinences of particular foods for limited periods of time, usually during recurring festivals. In regard to Isis and Magna Mater (and, presumably, Attis, her consort), we know that they abstained at times from foods made of grain. But in regard to the pagan mystery cults Pliny’s comment involved those who practiced dietary restrictions in conjunction with sexual abstinence.
The worship of Magna Mater and Attis involved a strong element of sexuality, but, during the March festival, as preliminary to the main event, devotees (not just priests) entered upon a nine-day period of fasting and abstinence that included denial of bread, wine, certain fowl and fruits, pork, and fish. In addition, they also refrained from sex. Consequently, worshippers of Magna Mater, at least in the month of March, combined fish and sex among their list of abstinences. But, Pliny speaks only of a restricted kind of fish (i.e. “fish without scales”, forgetting for a second that he is in error here). There is no such specification in the cult of Magna Mater of which I am aware. They presumably avoided fish of all kinds (with and without scales) during the nine-day period. Although worshippers of Isis did practice sexual abstinence in preparation for Isiac ceremonies, I have yet to find the same combination of sex and fish exclusions.
Jews would have had a high stake in knowing the ingredients of the fish sauce, because their abstention focuses specifically on the kind or kinds of fish used to produce the garum. Recognizing a sauce as castum, therefore, takes on more importance for them. Fish sauce producers, if they cared at all about catering to a specific clientele, even a small one, could, I think, have directed a specific product to them. So, since the restriction on scaleless fish is a stringent one, placing the adjective castum or casta on a fish sauce vessel would be critical for the Jewish customer. But, Pliny’s remark does not use the adjective castum to modify the garum; he merely indicates that there was a special garum for Jews because of the type of fish used. So the connection of the specific adjective castum with Jews is not certain. It remains possible that another adjective was used on vessels to attract Jewish consumers, or even that a totally different method was used to assure the Jews of the product’s acceptability (e.g., methods cited in the Talmud).
In sum, while I think that Pliny’s comments do refer to the existence of a kosher garum and that garum castum sold in Pompeii was most likely that product, doubts remain. Because of the uncertainty in our knowledge of pagan mystery cults and because Pliny’s reference cannot be corroborated in Greek, Latin, or Jewish sources, I am still not able to state unequivocally that the expression garum castum was meant exclusively for Jews.