Rabban Gamliel and Two Romans
There is a story found in a number of places in rabbinic literature which features a rabbi(s), Romans, and what were/are for some people, a number of problematic matters in Jewish law which seem to discriminate between Jews and non-Jews. I will bring one version of the story in full, pointing out the differences between the different versions. 
וכבר שלחה מלכות שני סרדיטיאות ואמרה להם לכו ועשו עצמכם יהודים וראו תורתם מה טיבה הלכו אצל רבן גמליאל לאושא וקראו את המקרא ושנו את המשנה מדרש הלכות והגדות בשעת פטירתם אמרו להם כל התורה נאה ומשובחת חוץ מדבר אחד זה שאתם אומרים גזילו של גוי מותר ושל ישראל אסור ודבר זה אין אנו מודיעים למלכות.
The government (of Rome) once sent out two officials, ordering them, “Go and disguise yourselves as Jews, and find out what is the nature of their Torah.” They went to Rabban Gamaliel at Usha, where they studied Scripture, Mishnah, Midrash, halakah and aggadah. As the officers were taking their leave, they said to the Sages, “All of the Torah is fine and praiseworthy, except for one thing, and that is your saying ‘That which is stolen from a non-Jew is permitted, while that which was stolen from a Jew is forbidden,’ but we will not report this exception to the government. (Sifre on Deuteronomy, Piska 344, trans. Reuven Hammer, p 356)
There are a number of differences between the different versions of the story and I will point out a few of them. The first is that according to the Babylonian Talmud, the two Romans studied with the generic “sages of Israel, while in the Sifre and the Jerusalem Talmud they studied with Rabban Gamliel. Many scholars identify him as Rabban Gamliel II, also known as Rabban Gamliel of Yavneh, despite one text of the Sifre associating him with Usha and not Yavneh. Another difference is with regard to the areas of Jewish law which the Romans found objectionable. In the Sifre, the only law mentioned is that one is not obligated to return the stolen property of a non-Jew. In the Babylonian Talmud the law mentioned is that when the ox of an Jew gors a non-Jew’s ox, the Jew is exempt from paying damages, while if the ox of a non-Jew gors the ox of an Jew, the non-Jew has to pay full damages.  In the Jerusalem Talmud there are two, or possibly three, laws mentioned: 1. That a Jewish woman is prohibited from helping a non-Jewish woman give birth, yet a non-Jewish woman helps a Jewish woman give birth; ; 2. That a Jewish woman is prohibited from nursing a non-Jewish child, yet a non-Jewish woman nurses a Jewish child;  3. That one is not obligated to return the stolen property of a non-Jew; 4. That when the ox of an Jew gors a non-Jew’s ox, the Jew is exempt from paying damages, while if the ox of a non-Jew gors the ox of an Jew, the non-Jew has to pay full damages. In the Jerusalem Talmud after no. 3 is brought, it says that “באותה שעה גזר רבן גמליאל על גזילת נכרי שיהא אסו’ מפני חילול השם” (“At that moment, Rabban Gamliel decried regarding the stolen property of a non-Jew [that it would forbidden] because of the profanation of God’s name”).
Both Gedaliah Alon and M.D. Herr read this story in the context of the attempt of Jewish courts and the Patriarch to receive official recognition.
These officials engage Rabban Gamliel in argument about whether Jewish law discriminates against gentiles. Apparently, then, their mission was somehow connected with the proposal to give status to the Jewish courts. 
It seems that discussions about the granting of some partial official recognition to the status of R. Gamliel of Jabneh, or at all events to the judicial status of the Jewish law courts led to the visit of military officials at his Academy in order to determine the nature of Jewish Law.
Saul Lieberman reads this story in the context of Jewish courts which existed in the diaspora with government recognition.
It is therefore natural to expect that the Roman government in Syria was interested in the fairness of Jewish civil law. A delegation was accordingly sent to the authoritative academy in Palestine to learn something about Jewish law…The delegation was primarily interested in Jewish civil law, as far as only Jews are concerned. All the unfair laws were limited to relations between Jew and Gentile. However, such cases would rarely come before the Jewish courts, as it is obvious from the character of these laws. The knowledge of such laws was outside the aim of their mission, since they had no practical application. The Roman delegation had no moral obligation to reveal these unfair laws to the government. 
Shaye Cohen reads the importance of the story a little differently. He translates “לכו ועשו עצמכם יהודים” as “Go and make yourselves Jews”, and not “Go and disguise yourselves as Jews”. Subsequently he says,
It is hard to imagine Romans pretending to be Jews, entering a rabbinic academy, there to study the entire rabbinic curriculum, without once blowing their cover or revealing their true identity. The accents, their looks, their initial ignorance of things Jewish and rabbinic (an ignorance that we may freely assume must have been quite impressive)-did none of this give them away? Apparently not.
If my analysis is correct, this story, as redacted by the editor of the Sifrei, told of Roman soldiers pretending to be Jews and successfully surviving the scrutiny of R. Gamliel and his colleagues. If you knew what to say and do, apparently it was easy to pass as a Jew. 
There was no need for the Roman soldiers to disguise themselves as Jews, because they all looked and sounded alike.
I think that the interpretation of the story which I find most compelling is that of Boaz Cohen. Cohen, while doubting the historical interpretations mentioned above, does see an authentic kernel to the story.
While the setting for this incident may be apocryphal, the criticism rings authentic. 
For Boaz Cohen, the most reliable part of the story may be the criticism which these two Romans made of certain discriminatory points of Jewish law. Cohen points out that these laws were similar to the laws of other nations in antiquity, but the criticism still had validity. There may have been some historical kernel to the story of which we have but an echo, but I do not think that a story such as this would have been preserved primarily in order to relay some information about a visit by Roman officials to the beit midrash. The larger questions about the relations between Jews and non-Jews as seen through the lens of Jewish law and how this is perceived by non-Jews loom too large and don’t allow us to limit the significance of this story solely to an event of possible political importance.
 The story appears in Sifre Devarim, Piska 344, p. 401 in ed. Finkelstein; Jerusalem Talmud Baba Kama 4:3, 4b; Babylonian Talmud Baba Kamma 38b. See the discussion of the different versions of this story by Catherine Hezser, Form, Function, and Historical Significance of the Rabbinic Story in Yerushalmi Neziqin, pp. 15-24.
 Mishnah Baba Kamma 4:3.
 Mishnah Avodah Zarah 2:1.
 Gedaliah Alon, The Jews in Their Land in the Talmudic Age: 70-640 C.E (70-640 C.E.), p. 121.
 M.D. Herr, “The Historical Significance of the Dialogues Between Jewish Sages and Roman Dignitaries”, Scripta Hierosolymitana, 22, 132-133.
 Saul Lieberman, “Achievements and Aspirations of Modern Jewish Scholarship”, Proceedings of the American Academy for Jewish Research, 46, 375-376.
 Shaye Cohen, The Beginnings of Jewishness: Boundaries, Varieties, Uncertainties, 38.
 Boaz Cohen, Jewish and Roman Law, p. 25.