The term ‘steel’ in the depth-psychology corpus is not a simple material referent but a carrier of multiple symbolic registers, each illuminating a different dimension of psychic and metaphysical experience. Its most theologically charged usage appears in John of Damascus, where steel figures as an analogy for the hypostatic union: fire permeates steel just as divinity permeates Christ’s humanity, transforming without dissolving natural properties. This image migrates productively into Hillman’s archetypal psychology, where iron—the raw precursor to steel—stands as the Martian metal, forged through rage, discipline, and repeated tempering. Hillman further notes that in eighteenth-century psychiatry, ‘Steel was already there in fantasy’: the material concretized psychic energies through mesmerists’ steel magnets and the emerging materialist brain science. Merleau-Ponty perceives steel’s ductility and hardness as phenomenologically visible, exemplifying synaesthetic inter-sensory perception. Harding’s visionary fantasy depicts swords of flaming steel as instruments of psychic conflict—a vivid dramatization of animus combat. Alchemically, the corpus links steel to the prima materia through the magnet–steel adamas dyad, in which hidden salt mediates philosophical transformation. Across these registers, steel embodies hardness, penetration, transformation under heat, and the paradox of a substance that can be both the vehicle and the limit of transmutation.