Of the numerous conjectures about the origin of the name Armilus, the most probable is that it is derived from Romulus (founder of Rome, with Remus), although other suggestions are that it may be a corruption of Angra-Mainyu, the Persian god of evil, or from the Greek 'Arimanoj (Ahriman). The legend that he was born of a beautiful virgin (see below) likewise connects it with Rome. It is most likely that as a result of the sufferings of the Jews at the hands of the Romans at the time of the destruction of the Second Temple, and during and after the Bar Kokhba War, and especially after Christianity had conquered the Roman Empire and initiated a ruthless persecution of Judaism from which it had sprung, the Jews began to regard Rome, founded by Romulus, as the kingdom of Satan, the antithesis of the kingdom of Heaven. Hence they applied the name of Armilus to that diabolic power which had gained a transient, terrestrial victory (in contrast to the celestial and eternal kingdom of the Messiah).
Armilus and his evil deeds are described in detail only in the above-mentioned later Hebrew Midrashim now republished with detailed introduction and valuable notes, by J. Even Shemuel (Kaufmann) in his Midreshei Ge'ullah (1942, 19442). Armilus is the least of the kings, the son of a bondwoman, and monstrous in appearance (Midreshei Ge'ullah, Sefer Eliyahu, 42; Yemot ha-Mashi'ah, 96–97; Nistarot shel R. Shimon b. Yohai, 4, 195; see also textual variants, 382b, 402). He is frequently referred to briefly as "the son of a stone." This brief reference is fully explained in a legend: "They tell that in Rome there is a marble statue of a beautiful maiden, fashioned not by human hand but by the Holy One blessed be He, who created it in His might. The wicked of the nations of the world, the sons of Belial, come and warm her and lie with her, and He preserves their seed within the stone from which He creates a being and forms it into a child, whereupon she splits asunder and there issues from her the likeness of a man whose name is the Satan Armilus, whom the Gentiles call Antichrist. He is 12 cubits tall and two cubits broad, there is a span between his eyes which are crooked and red, his hair is golden-colored, the soles of his feet are green, and he has two heads" (Pirkei ha-Mashi'ah, in Midreshei Ge'ullah, p. 320). This Armilus will deceive the whole world into believing that he is God and will reign over the entire world. He will come with ten kings and together they will fight over Jerusalem, and Armilus will slay Nehemiah b. Hushi'el, who is Messiah the son of Joseph, as well as many righteous men with him, and "Israel will mourn for him as one that is in bitterness for his only son" (cf. Zech. 12:19–12). Armilus will banish Israel "to the wilderness" and it will be a time of unprecedented distress for Israel: there will be increasing famine, and the Gentiles will expel the Jews from their lands, and they will hide in caves and towers. Armilus will conquer not only Jerusalem but also Antioch (the capital of Syria, where non-Jewish Christianity originated—Acts 11:26). "He will take the stone from which he was born," and make her "the chief of all idolatry." All the Gentiles will bow down to her, burn incense and pour out libations to her, "and whosoever will venture to look upon her will be unable to do so, for no man can look upon her face by reason of her beauty" (Sefer Zerubbavel, in Midreshei Ge'ullah, p. 80ff.). The legendary "marble virgin" is based on the fable current in the Middle Ages, and associated with the name of Virgil, that in Rome there was a stone statue of a virgin with which the Romans had immoral relations, though it also probably contains elements of the immaculate conception and the Christian worship of images.
God will war against the host of Armilus (or of Gog and Magog), and all this host and all Judah's enemies will perish in the valley of Arbel. 500 men of Israel, with Nehemiah and Elijah at their head, will defeat 500,000 of the host of Armilus. Then there will be a great deliverance for Israel and the kingdom of Heaven will spread over all the earth.
These are the main features of the Armilus legend, as contained in Sefer Zerubbavel. In the other smaller Midrashim and in the works of Saadiah Gaon and Hai Gaon there are variants and addenda. All these legends, that embody the beautiful and the moral as well as the curious and the coarse, originated from an intermingling of Persian, Roman, and Christian beliefs with an ancient Jewish tradition concerning "messianic birthpangs" which would precede the messianic age and during which Messiah the son of Joseph would be killed by Romulus-Rome, even as Bar Kokhba was killed by Rome, which had adopted the belief, so strange in Jewish eyes, in a holy virgin and in beautiful stone images. The yearning for the downfall of Christian Rome, which persecuted Israel after adopting its Torah, gave rise to the legend of Armilus, the anti-Messiah, who would multiply evils upon Israel. But Messiah the son of David would vanquish him (that is, Romulus-Rome) and bring the kingdom of Heaven upon earth.