<p>This study investigates the exceptional corrosion resistance of ancient Indian iron artifacts, revealing advanced metallurgical strategies that contributed to their longevity. Key examples include the Delhi Iron Pillar (c. 400 CE), Dhar Iron Pillar (c. 1010–1053 CE), and the iron beams of the Sun Temple in Konark (c. 1250 CE), which exhibit remarkable atmospheric durability despite centuries of exposure. The findings highlight the crucial role of high-phosphorus and low-sulfur content in promoting the formation of protective iron-hydrogen phosphate hydrate layers, passivating the metal surface and mitigating corrosion. Advanced analytical techniques, including micro-XRD, Raman spectroscopy, and SEM-EDS, identify a multi-phase corrosion system comprising amorphous δ-FeOOH (misawite), goethite (α-FeOOH), magnetite (Fe₃O₄), lepidocrocite (γ-FeOOH), and akaganeite (β-FeOOH). These corrosion products form layered protective structures akin to those found in modern weathering steels. Environmental factors such as humidity, temperature, and chloride exposure significantly influence corrosion behavior. For instance, while the Delhi Iron Pillar benefits from Delhi’s arid climate, the iron clamps at Deogarh Temple (c. 600 CE) and the Thanjavur Cannon (seventeenth century) demonstrate resilience in high-humidity, salt-laden environments. The Adi-Mookambika Iron Pillar at Kollur exemplifies outstanding corrosion resistance in a coastal setting. Its moderate phosphorus content fosters the formation of a stable, magnetite-rich protective oxide layer, limiting moisture infiltration despite prolonged exposure to monsoon rains and saline winds. The pillar’s ferrite–pearlite microstructure, combined with extensive hammer forging, enhances structural integrity by reducing oxidation pathways. This comparative analysis confirms that the corrosion resistance of ancient Indian iron was a deliberate outcome of material selection, forging techniques, and environmental adaptation. The findings provide valuable insights into modern alloy design, corrosion-resistant material development, and heritage conservation. Future research should focus on long-term corrosion modeling, microstructural analysis of lesser-characterized artifacts using advanced techniques such as atom probe tomography, and the application of ancient metallurgical principles to contemporary materials engineering for the development of sustainable, durable alloys.</p>