That combination, a named feature with a known documentary presence but no confirmed location, places it in a curious category of things that were real enough to be written down and mapped, yet have since slipped entirely from view.

The Iron Dam appears in the record through two related sources. The first is the Riding of the Franchises of 1603, a formal civic perambulation of Dublin's boundary markers, the notes from which were later compiled by the archivist and historian J. T. Gilbert in his Calendar of Ancient Records of Dublin. The riding of franchises was a periodic ceremonial and administrative practice in which city officials physically walked or rode the boundaries of municipal jurisdiction, pausing at landmarks to reaffirm them in the collective memory. That the Iron Dam was significant enough to be named during such a perambulation suggests it served as a recognised boundary point. The structure is also noted on the Down Survey composite maps for County Dublin, produced between 1655 and 1656 under the direction of William Petty, a remarkably detailed land survey carried out in the aftermath of the Cromwellian conquest. A dam, in the context of early modern Dublin, would most likely have been a feature controlling water flow, possibly on one of the city's many mill streams or watercourses that have since been culverted or redirected beyond recognition. The qualifier "iron" is intriguing but unexplained in the surviving notes.

Because the Iron Dam has not been precisely located by researchers working from the Gilbert calendar or the Down Survey materials, there is no site to visit in any conventional sense. What the record offers instead is a prompt to look more carefully at the northern city's older watercourses and to consider how much civic infrastructure has vanished beneath streets and development over four centuries. Anyone with an interest in historical cartography might explore digitised versions of the Down Survey maps, which are held and made available through Irish archival institutions, and trace the watercourses marked in the Dublin north city sheet to see where a controlling structure might have sat.