Step 1: Bringing Scientific Methodology and Military Precision:
Sir Robert Eric Mortimer Wheeler (R.E.M. Wheeler) assumed the office of Director General of the Archaeological Survey of India (ASI) in $1944$. He brought with him extensive military experience and systematic scientific discipline, which transformed the loose excavation practices of Indian archaeology into a rigorous scientific field.
Step 2: Shifting from Horizontal digging to Stratigraphy:
Before Wheeler's tenure, excavations in India were largely carried out along mechanical, uniform horizontal lines, which grouped artifacts from different historical periods together. Wheeler recognized that this ignored the tural deposition of earth. He introduced the scientific method of digging along the geological/archaeological stratigraphy (soil layers). This allowed archaeologists to correlate artifacts with their exact timeline of deposition, correcting major chronological errors.
Step 3: Pioneering Discoveries at Indus Valley Sites:
Wheeler worked extensively on Harappan sites. He identified and excavated the massive fortification walls surrounding the citadel at Harappa. He also attempted to bridge archaeological evidence with literary sources (such as correlating Harappa's destruction with the Rigvedic mentions of puras and the deity Indra as Purandara or fort-destroyer), bringing global scholarly attention to India's oldest civilization.