Eliezer ben Nathan (Hebrew: אליעזר בן נתן) of Mainz (1090–1170), or Ra'avan (ראב"ן‎), was a halakist and liturgical poet.

[1] Even haEzer is a collection of responsa, found in two sections at the beginning and end of the work, and legal decisions, arranged in the middle as a commentary to the Babylonian Talmud.

This book, which Eliezer compiled from smaller topical pamphlets, was also known as Tzaf'nat Paneah in the medieval period and continues to be called Sefer Ra'avan.

They contain precise statements of the prices of goods and accurate information concerning commercial usages in the Rhineland and in distant Slavic countries; e.g., concerning the golden trade routes in Strasburg and Speyer (fol.

119) even presenting a connected commentary on Proverbs 30:1-6, in which Saadia Gaon's view is cited—namely, that Isthiel and Ucal were the names of two men who addressed philosophical questions to Agur ben Jakeh.

Not until its importance had been specially urged by the most influential rabbis of Poland—Mordecai Jafe, Samuel Eliezer Edels (Maharsha), Solomon Ephraim Luntschitz, among others, in a formal appeal issued from Posen in 1609—was its publication undertaken.

With their allusions to haggadic interpretations, their employment of payyeṭan phraseology, acrostics, rimes, and similar mechanical devices, they differ little from many other liturgical productions.

Thus, one piyyuṭ composed for a circumcision occurring on the Sabbath bears at the close the cipher "ABN," and the words "Long live my child Eliakim."

In deference to a passage in Joseph ha-Kohen's Emek haBacha, p. 31, which makes a certain Eleazar ha-Levi the author, some writers (as Landshuth and H. Grätz) have denied Eliezer's authorship of this chronicle.

The chronicle was first edited by Adolph Jellinek;[6] and was republished as Hebräische Berichte über die Judenverfolgungen Während der Kreuzzüge, by A. Neubauer and Stern, together with a German translation.