The Indus Valley Civilization was a Bronze Age civilization in the northwestern regions of South Asia that flourished approximately from 2600 BC to 1900 BC. One of the earliest urban cultures of the ancient world, it was contemporaneous with ancient Egypt and Mesopotamia. It featured advanced urban planning, sophisticated drainage systems, standardized weights and measures, and a writing system that remains undeciphered. Major urban centers included Harappa and Mohenjo-daro, discovered in the 1920s by archaeologists Daya Ram Sahni and R.D. Banerji respectively.