The Iron Pillar of Delhi is a 7-meter-tall iron column located in the Qutb complex in Delhi, India. It is believed to have been constructed during the Gupta period in the 4th or 5th century AD, and is known for its remarkable resistance to corrosion.

The pillar is made of a high-purity iron alloy, and features inscriptions in the Brahmi script that refer to a ruler named Chandra. Despite being exposed to the elements for over a millennium, the pillar has not rusted or deteriorated significantly, which is a testament to the advanced metallurgical techniques employed by ancient Indian blacksmiths.

Numerous theories have been proposed to explain the pillar's remarkable resistance to corrosion, including a protective layer of rust, a high phosphorus content in the iron, and the presence of trace elements such as nickel and chromium. However, the exact reason for the pillar's durability remains a subject of debate and investigation.

The Iron Pillar of Delhi is considered a remarkable feat of ancient engineering, and continues to be a popular tourist attraction and an object of scientific study.