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date: 01 December 2020

There is little evidence of conversion to Israelite religion or Judaism in Jewish scriptures. For instance, while later rabbis understood the book of Ruth to portray the conversion of Ruth to Judaism, the book itself repeatedly refers to her as a Moabite, even after she declares to her mother-in-law Naomi that “your people will be my people, and your God will be my God” (Ruth 1:16). Similarly, the Hebrew text of Esther 8:17 portrays numerous Gentiles Judaizing: “Many peoples of the land Judaized because fear of the Jews fell upon them.” The Septuagint translation (LXX) adds that this “Judaization” included circumcision. While some scholars believe that this verse refers to conversion, the author claims that this action was taken only out of fear of the Jews. These Gentiles did not Judaize out of religious conviction; rather, they merely pretended to be Jews to avoid Jewish retaliation for the violent machinations of Haman.1 Other scholars point to the LXX use of the term prosēlytos to translate the Hebrew word ger (“resident alien”), arguing that LXX translators understood the ger to be a full-fledged convert to Judaism.2 Nonetheless, papyrological evidence and an adequate understanding of translation technique in the LXX confirm that prosēlytos refers only to a resident alien, not to a religious convert.3

Shaye Cohen has argued convincingly that conversions to Judaism began to occur in the 2nd century bce, as the Hasmoneans came to power and developed an understanding of Jewishness that permitted people to adopt Jewish customs and thus acquire Jewish identity. It is possible that the Hasmonean ultimatum to the Idumeans and Itureans—that they adopt Jewish customs or vacate land that had fallen under Hasmonean control—implied this new understanding of Jewish identity that allowed Gentiles to become Jews. (For the Idumeans, see Josephus, Ant. 13.258; War 1.63; and Strabo, Geography 16.2.34. For the Itureans, see Josephus, Ant. 13.318–319.) While scholars dispute whether this compelled adoption of Jewish customs can accurately be called “conversion,” it appears that many early Jews understood such Idumeans and Itureans to be converts.4

The book of Judith, which dates to the 2nd century bce, clearly envisages Achior the Ammonite entering into the nation of Israel through the rite of circumcision (14:10). Strikingly, Achior’s ethnicity should preclude him from ever being able to join the community of Israel, since Deuteronomy 23:3 states, “No Ammonite or Moabite shall enter into the assembly of Yhwh.” In spite of this prohibition, the author uses the same language of Achior that Genesis uses of Abraham: both Abraham and Achior trust in God and then circumcise the flesh of their foreskins (cf. Genesis 15:6, 17:24). The book of Judith, then, serves as the earliest evidence both for understanding Abraham as a proto-convert to Judaism and for positively portraying a non-Jew converting to Judaism.5

According to 2 Maccabees, after Antiochus persecuted Jews for their ancestral customs, God tormented him by plaguing his body with worms. The pain of this experience led Antiochus to try to convert to Judaism on his deathbed: not only does he promise that he would become a Jew, he also promises to declare God’s power to all inhabited places (9:17), if only God would end his suffering. Nevertheless, his suffering continues, suggesting that his promise of a deathbed conversion fails to impress Israel’s God.

Joseph and Aseneth also portrays the conversion of a Gentile to Judaism.6 In justifying Joseph’s marriage to Aseneth, the daughter of the Egyptian priest of On (Genesis 41:25), the author skillfully portrays Aseneth’s miraculous conversion from an idolatrous Egyptian woman to a pious Israelite woman. Her eight-day transformation process mimics the eighth-day circumcision of the newborn Jewish male (Genesis 17:12, 14; Leviticus 12:3). This transformation overcomes both her Egyptian ethnicity and her idolatrous past, enabling her to marry the patriarch Joseph without implicating him in exogamy.7 Further, the work envisages other non-Jews coming to Israel’s God, “taking shelter under Aseneth’s wings” (15:7).

In the 1st century ce, Philo of Alexandria portrays converts to Judaism as leaving behind a life of vice for a life of virtue. In this, he is responding to the larger Greco-Roman question concerning which way of life or philosophy liberates humans from desire in order to live self-controlled, virtuous lives.8 For instance, in On the Virtues, Philo claims that, upon taking up observance of the Jewish law, “proselytes [epēlutai] become at once temperate, continent, modest, gentle, kind, humane, serious, just, high-minded, truth-lovers, superior to the desire for money and pleasure.”9 In fact, Philo argues that, among its many benefits, the rite of circumcision functions as “the excision of pleasures that bewitch the mind. For since among the delights of pleasure the highest is held by the intercourse of man and woman, the lawmakers thought it good to cut the organ that serves such intercourse, thereby making circumcision the figure of the excision of excessive and superfluous pleasure, not only of one pleasure but of all the other pleasures signified by one, and that the strongest” (Special Laws 1.9; cf. Philo, QG 3.47–48).

Also in the 1st century, Josephus relates the conversion of Izates, king of Adiabene (Ant. 20.17–47). At the behest of Eleazar, who was likely a Pharisee given Josephus’s description of him as being a precise interpreter of the law (Ant. 20.43; cf. Life 191; War 1.108, 110), Izates undergoes circumcision.10 Josephus also refers to a number of Gentiles who, in his words, “Judaize.” For instance, upon being captured, Metilius, the commander of the Roman garrison stationed in Jerusalem, vows to undergo Judaization to the point of circumcision (War 2.454). Likewise, he mentions numerous Syrians who had Judaized, although he neither clarifies the way in which these Syrians had Judaized, nor describes the degree to which they had been incorporated into the Jewish community in Syria (War 2.462–463).

The Gospel of Matthew portrays Jesus indicting Pharisees and scribes for what appears to be their missionizing efforts: “Woe to you, scribes and Pharisees—hypocrites—for you cross sea and land to make one proselyte, and you make him become twice as much a son of Gehenna as yourselves” (23:15). Most interpreters take this statement as a reference to the efforts of some Pharisees to convert Gentiles to Judaism. This evidence, however, is disputed: it is possible that the statement refers to the desire of Pharisees to convince other Jews to adhere to their form of Judaism.11 The Acts of the Apostles lends support to the suggestion that Matthew’s Jesus refers to proselytism of Gentiles. At the Jerusalem Council, according to Luke, some Christ-following Pharisees demand that Jewish Christ followers require Gentiles to observe the Jewish law: “It is necessary to circumcise them and to instruct them to keep the law of Moses” (Acts 15:5). The claim that Gentile followers of Jesus should adopt the Jewish law (i.e., convert) provided the occasion for Paul’s letters to the Galatians, Romans, and Philippians.

Non-Jewish Greco-Roman writers also provide evidence of Gentile conversion. Juvenal ridicules those who, building on their fathers’ observance of the Jewish Sabbath and dietary laws, undergo circumcision. He finds it ludicrous that Romans would reject their own laws for those of the Jews (Satires 14.96–106). Tacitus too laments the fact that some people despise their own ancestral customs, undergo circumcision, and keep themselves separate from others (Histories 5.5.1–2). According to Augustine (City of God 6.11), Seneca claims in his lost work On Superstition that Jewish customs had spread throughout the Roman Empire (cf. Seneca, Moral Letters 108.22). These non-Jewish writers demonstrate that the phenomenon of non-Jews becoming Jews was relatively common and well known. They also give voice to what was no doubt a common view: non-Jews who adopted Jewish customs and became Jews were despised because of the lack of esteem they had for their own people, customs, and gods.

Finally, epigraphic evidence from the ancient Mediterranean world confirms the existence of converts to Judaism, for there are about twenty individuals referred to as proselytes in inscriptions dating from the 1st century bce to the mid-2nd century ce. These inscriptions can be found in numerous locations—Rome, Venosa, Jerusalem, Caesarea Maritima, Cyrene, Aphrodisias, and Dura Europas—demonstrating the widespread phenomenon of Gentiles who converted to Judaism.12

Nonetheless, not all Jews in the Greco-Roman period believed that Gentiles should or even could convert to Judaism. Already in the Persian period, Ezra-Nehemiah promotes an ideology of exclusion with regard to Gentiles. These writings portray anxiety over intermarriage between Jewish men and non-Jewish women. Irrespective of the religious commitments of these women and the children produced by such unions, the author depicts the Jewish leaders requiring that Jewish men extricate themselves from these marriages, expelling the foreign women and the offspring of mixed ethnic descent. The authors of these works hold to a theology that envisages a sharp genealogical distinction between Israel, the holy seed, and the Gentiles, the profane seed (Ezra 9:2).13

In the 2nd century bce, the author of Jubilees further promotes this holy-seed ideology. Jacob’s seed is ontologically distinct from the other nations; it alone can observe the holy Sabbath (“The Creator of all blessed it, but he did not sanctify any people or nation to keep the Sabbath thereon with the sole exception of Israel. He granted to them alone that they might eat and drink and keep the Sabbath thereon upon the earth,” Jub. 2.31) and the rite of circumcision (“Anyone who is born whose own flesh is not circumcised on the eighth day is not from the sons of the covenant which the LORD made for Abraham,” Jub. 15.26). Through his insistence on eighth-day circumcision, the author makes conversion to Judaism an impossibility.14

Early literature of Christ followers indicates that this stream of Judaism also debated the value or even possibility of conversion to Judaism. The apostle Paul claims that he used to preach circumcision, suggesting that he once advocated that Gentiles become Jews through the rite of circumcision (Galatians 5:11). His letters to Galatia, Corinth, Philippi, and Rome indicate that other Christ followers still thought that Gentiles needed to become Jews. Such thinking is given voice in the narrative of Acts, which portrays some Christ-following Pharisees concluding that Gentiles needed to undergo circumcision and adopt the law of Moses (Acts 15:5). According to both the author of Acts and the apostle Paul, though, Gentiles did not need to convert to Judaism in order to be saved. In fact, it is possible that both thought that Gentiles simply could not convert to Judaism at all.15

Early rabbinic literature presents the concept of conversion developed most fully and explicitly. The Mishnah and Tosefta preserve a story in which the rabbis debate whether an Ammonite by the name of Judah can become a Jew, despite the prohibition of Deuteronomy 23 (m. Yad. 4.4; cf. t. Yad. 2.17–18; b. Ber. 28a). They conclude that he indeed can become a Jew. Mekhilta de-Rabbi Ishmael depicts Abraham’s circumcision at the age of ninety-nine as a paradigmatic conversion: “Beloved are the proselytes. It was for their sake that our father Abraham was not circumcised until he was ninety-nine years old. Had he been circumcised at twenty or at thirty years of age, only those under the age of thirty could have become proselytes” (Nezikin 18). Finally, the Babylonian Talmud gives evidence of a fully expressed view that the convert to Judaism undergoes an essential change, in effect becoming like a newborn Jew (b. Yeb. 22a; 48b; 62a; 97b; b. Bek. 47a).16


  • Blaschke, Andreas. Beschneidung: Zeugnisse der Bibel und verwandter Texte. Texte und Arbeiten zum neutestamentlichen Zeitalter 28. Tübingen, Germany: Francke Verlag, 1998.
  • Chesnutt, Randall. From Death to Life: Conversion in Joseph and Aseneth. Sheffield: Sheffield Academic Press, 1995.
  • Cohen, Shaye J. D. “Conversion to Judaism in Historical Perspective: From Biblical Israel to Postbiblical Judaism.” Conservative Judaism 36 (1983): 31–45.
  • Cohen, Shaye J. D. The Beginnings of Jewishness: Boundaries, Varieties, Uncertainties. Berkeley: University of California Press, 1999.
  • Crook, Zeba A. Reconceptualising Conversion: Patronage, Loyalty, and Conversion in the Religions of the Ancient Mediterranean. Berlin: Walter de Gruyter, 2004.
  • Donaldson, Terence L. Judaism and the Gentiles: Jewish Patterns of Universalism (to 135 CE). Waco, TX: Baylor University Press, 2007.
  • Feldman, Louis H. “Was Judaism a Missionary Religion in Ancient Times?” In Jewish Assimilation, Acculturation and Accommodation: Past Traditions, Current Issues and Future Prospects. Edited by Menachem Mor, 24–37. Lanham, MD: University Press of America, 1992.
  • Feldman, Louis H. Jew and Gentile in the Ancient World: Attitudes and Interactions from Alexander to Justinian. Princeton, NJ: Princeton University Press, 1993.
  • Goodman, Martin. Mission and Conversion: Proselytizing in the Religious History of the Roman Empire. Oxford: Clarendon, 1994.
  • Hayes, Christine E. Gentile Impurities and Jewish Identities: Intermarriage and Conversion from the Bible to the Talmud. Oxford: Oxford University Press, 2002.
  • Lavee, Moshe. “The ‘Tractate’ of Conversion—BT Yeb. 46–48 and the Evolution of Conversion Procedure.” European Journal of Jewish Studies 4 (2010): 169–213.
  • Mimouni, Simon C. La circoncision dans le monde judéen aux époques grecque et romaine: Histoire d’un conflit interne au judaïsme. Leuven: Peeters, 2007.
  • Nock, A. D. Conversion: The Old and the New in Religion from Alexander the Great to Augustine of Hippo. London: Oxford University Press, 1933.
  • Porton, Gary G. The Stranger within Your Gates: Converts and Conversion in Rabbinic Judaism. Chicago: University of Chicago Press, 1994.
  • Sagi, Avi, and Zvi Zohar, Transforming Identity: The Ritual Transition from Gentile to Jew—Structure and Meaning. London: Continuum, 2007.
  • Schwartz, Daniel R. “Doing Like Jews or Becoming a Jew? Josephus on Women Converts to Judaism.” In Jewish Identity in the Greco-Roman World/Jüdische Identität in der griechischrömischen Welt. Edited by Jörg Frey, Daniel R. Schwartz, and Stephanie Gripentrog, 93–109. Leiden: Brill, 2007.
  • Thiessen, Matthew. Contesting Conversion: Genealogy, Circumcision, and Identity in Ancient Judaism and Christianity. New York: Oxford University Press, 2011.
  • Thiessen, Matthew. Paul and the Gentile Problem. New York: Oxford University Press, 2016.


  • 1. Shaye J. D. Cohen, The Beginnings of Jewishness: Boundaries, Varieties, Uncertainties (Berkeley: University of California Press, 1999), 181–182.

  • 2. W. C. Allen, “On the Meaning of ΠΡΟΣΗΛΥΤΟΣ‎ in the Septuagint,” The Expositor 4 (1894): 264–275.

  • 3. See David M. Moffitt and C. Jacob Butera, “P.Duk. inv. 727r: New Evidence for the Meaning and Provenance of the Word Προσήλυτος‎,” JBL 132 (2013): 159–178, and Matthew Thiessen, “Revisiting the προσήλυτος‎ in ‘the LXX,’” JBL 132 (2013): 333–350.

  • 4. Doron Mendels (The Land of Israel as a Political Concept in Hasmonean Literature: Recourse to History in Second Century b.c. Claims to the Holy Land [Tübingen, Germany: Mohr Siebeck, 1987], 57–81) and Martin Goodman (Mission and Conversion: Proselytizing in the Religious History of the Roman Empire [Oxford: Clarendon, 1994], 74–76) argue that the Idumeans and Itureans took up Jewish practices out of compulsion, while Aryeh Kasher (Jews, Idumaeans, and Ancient Arabs: Relations of the Jews in Eretz-Israel with the Nations of the Frontier and the Desert during the Hellenistic and Roman Era [332 BCE–70 CE] [Tübingen, Germany: Mohr Siebeck, 1988], 46–77) and Cohen (The Beginnings of Jewishness, 116–117) argue that they willingly took up Jewish practices.

  • 5. Deborah Levine Gera, Judith (Berlin: de Gruyter, 2014), 421.

  • 6. Contrary to the majority of interpreters, Ross Shepard Kraemer (When Aseneth Met Joseph: A Late Antique Tale of the Biblical Patriarch and his Egyptian Wife, Reconsidered [Oxford: Oxford University Press, 1998]; and Rivka Nir (Joseph and Aseneth: A Christian Book [Sheffield: Sheffield Phoenix, 2012]) argue that the work is Christian. On the Jewish authorship of the work, see Gideon Bohak, Joseph and Aseneth and the Jewish Temple at Heliopolis (Atlanta: Scholars, 1996).

  • 7. See Matthew Thiessen, “Aseneth’s Eight-Day Transformation as Scriptural Justification for Conversion,” JSJ 45 (2014): 229–249.

  • 8. See Martha C. Nussbaum, The Therapy of Desire: Theory and Practice in Hellenistic Ethics (Princeton, NJ: Princeton University Press, 1994), and John T. Fitzgerald, ed., Passions and Moral Progress in Greco-Roman Thought (New York: Routledge, 2008).

  • 9. See Ellen Birnbaum, The Place of Judaism in Philo’s Thought: Israel, Jews, and Proselytes (Atlanta: Scholars Press, 1996).

  • 10. On this story, see Daniel R. Schwartz, “God, Gentiles, and Jewish Law: On Acts 15 and Josephus’ Adiabene Narrative,” in Geschichte—Tradition—Reflexion: Festschrift für Martin Hengel zum 70. Geburtstag, 3 vols., eds. Hubert Cancik, Hermann Lichtenberger, and Peter Schäfer (Tübingen, Germany: Mohr Siebeck, 1996), 1:263–282, and Mark D. Nanos, “The Question of Conceptualization: Qualifying Paul’s Position on Circumcision in Dialogue with Josephus’s Advisors to King Izates,” in Paul within Judaism: Restoring the First-Century Context to the Apostle, eds. Mark D. Nanos and Magnus Zetterholm (Minneapolis: Fortress, 2015), 105–152.

  • 11. See Alan F. Segal, “The Cost of Proselytism and Conversion,” in Society of Biblical Literature 1988 Seminar Papers (Atlanta: Scholars Press, 1988), 336–369, and Goodman, Mission and Conversion, 70.

  • 12. See Pau Figueras, “Epigraphic Evidence for Proselytism in Ancient Judaism,” Immanuel 23/25 (1990): 194–206, and Terence L. Donaldson, Judaism and the Gentiles: Jewish Patterns of Universalism (to 135 CE) (Waco, TX: Baylor University Press, 2007), 437–466.

  • 13. Matthew Thiessen, “The Function of a Conjunction: Inclusivist or Exclusivist Strategies in Ezra 6.19–21 and Nehemiah 10.29–30?” JSOT 34 (2009): 63–79.

  • 14. See Christine E. Hayes, Gentile Impurities and Jewish Identities: Intermarriage and Conversion from the Bible to the Talmud (Oxford: Oxford University Press, 2002), 73–81; and Thiessen, Contesting Conversion: Genealogy, Circumcision, and Identity in Ancient Judaism and Christianity (New York: Oxford University Press, 2011), 67–86.

  • 15. See Thiessen, Contesting Conversion, 111–141, and Thiessen, Paul and the Gentile Problem (New York: Oxford University Press, 2016).

  • 16. See Gary G. Porton, The Stranger within Your Gates: Converts and Conversion in Rabbinic Judaism (Chicago: University of Chicago Press, 1994); and Moshe Lavee, “The ‘Tractate’ of Conversion—BT Yeb. 46–48 and the Evolution of Conversion Procedure,” EJJS 4 (2010): 169–213.