| Summary: | The technology of using metallic iron (Fe<sup>0</sup>) for in situ generation of iron oxides for water treatment is a very old one. The Fe<sup>0</sup> remediation technology has been re-discovered in the framework of groundwater remediation using permeable reactive barriers (PRBs). Despite its simplicity, the improvement of Fe<sup>0</sup> PRBs is fraught with difficulties regarding their operating modes. The literature dealing with Fe<sup>0</sup> remediation contains ambiguities regarding its invention and its development. The present paper examines the sequence of contributions prior to the advent of Fe<sup>0</sup> PRBs in order to clarify the seemingly complex picture. To achieve this, the current paper addresses the following questions: (i) What were the motivations of various authors in developing their respective innovations over the years?, (ii) what are the ancient achievements which can accelerate progress in knowledge for the development of Fe<sup>0</sup> PRBs?, and (iii) was Fe<sup>0</sup> really used for the removal of organic species for the first time in the 1970s? A careful examination of ancient works reveals that: (i) The wrong questions were asked during the past three decades, as Fe<sup>0</sup> was premised as a reducing agent, (ii) credit for using Fe<sup>0</sup> for water treatment belongs to no individual scientist, and (iii) credit for the use of Fe<sup>0</sup> in filtration systems for safe drinking water provision belongs to scientists from the 1850s, while credit for the use of Fe<sup>0</sup> for the removal of aqueous organic species does not belong to the pioneers of the Fe<sup>0</sup> PRB technology. However, it was these pioneers who exploited Fe<sup>0</sup> for groundwater remediation, thereby extending its potential. Complementing recent achievements with the chemistry of the Fe<sup>0</sup>/H<sub>2</sub>O system would facilitate the design of more sustainable Fe<sup>0</sup>-remediation systems.
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