Archaeologists recently uncovered a seven-metre-thick defensive wall at Mohenjo-daro, one of the significant ancient cities of the Indus Valley Civilization in the Sindh province of Pakistan. The fresh excavation aimed to figure out the overall plan and chronology of the mud-brick city wall that surrounds what is called the western Stupa Mound.
Significantly, new radiocarbon dating confirmed an earlier urban occupation at Mohenjo-daro during the Kot Diji or Early Harappan Phase, 3300-2600 BC, read a statement issued by Sindh Directorate General Antiquities and Archaeology (DGAA). When the remains were first discovered by British archaeologist and officer in the British Army, Mortimer Wheeler, in 1950, they were dated to 2800-2600 BC. The latest dating pushes back their antiquity further.
DGAA stated that the new excavations at the plain level to the west of the famous Stupa Mound had provided five new radiocarbon dates for a massive mud-brick perimeter wall of the city, which was misidentified it as a revetment or "bund" built to protect the city from flooding by Wheeler.
During previous attempts, excavation teams were unable to reach the natural soil level due to the presence of groundwater. Although the lowest levels are still below the water table, the earlier trench of Wheeler was reopened by DGAA, which undertook the study jointly with the Sindh Exploration and Adventure Society (SEAS).
The efforts yielded significant results and brought to light more key features of the site. According to DGAA, pottery and carbon samples from the lowest levels of the first wall indicate that this initial structure was constructed at the end of the Early Harappan or Kot Diji Phase around 2700-2600 BCE, approximately 100 years before the beginning of the Harappan Phase.
“Kot Dijian pottery recovered from new deep coring below the first city wall indicates the presence of a substantial Early Harappan occupation before the first city wall was constructed. These findings correspond with the results from excavations at the site of Harappa, Punjab (in Pakistan), which also has an Early Harappan, Kot Dijian Phase occupation and city wall dating to around 2800-2600 BCE,” the department stated.
Discovery of unknown layers
On the significance of the discovered rampart, renowned field archaeologist B R Mani, known for his extensive work on Harappan (Indus Valley) Civilization sites, said that the findings point to previously unexplored early layers of the place. “Earlier excavations could not reach the natural soil level due to water seepage, which limited our understanding of its earliest phases. Now, with deeper exploration, early evidence is beginning to emerge,” he said.
Mani also noted that similar early cultural layers had already been identified at Harappa and at Indian sites such as Kalibangan and Kunal. “This shows that urban development did not occur suddenly, but evolved gradually across multiple sites… There has been a gradual development. Till now, what we knew about Mohenjo-daro, we knew about mature Harappan. Now, we have got to the early stage. This is the importance,” he said. Mani’s last posting was at the National Museum in New Delhi as its director general.
Kalibangan (Rajasthan) and Kunal (Haryana) are early Indus Valley Civilization sites showcasing pre-Harappan (3500–2500 BC) and mature Harappan phases.
Disha Ahluwalia, archaeologist and junior research fellow at the Indian Council of Historical Research (ICHR), echoed Mani, saying the discovery tells us about an unidentified early stratum at Mohenjo-daro. “This particular level was not known. It was understood through the earlier excavations of Mohenjo-daro. It only has one phase, which is the urban phase, which means that the span of the occupation is about 800 years and not more. The new findings sort of shows that it goes beyond 800 years, it goes to the early formative phases as well.”
Ancient planned urban centre
As per the brief about the site on the Unesco portal, the archaeological ruins at Mohenjo-daro, which means mound of the dead, are the best preserved urban settlement in South Asia dating to the beginning of the 3rd millennium BC. The remnants are located on the right bank of the Indus River; 28 km from Larkana city in Sindh Province. “The property represents the metropolis of Indus Civilization, which flourished between 2,500-1,500 BC in the Indus valley and is one of the world’s three great ancient Civilizations,” it states.
The discoveries at the site over the last 100 years provide valuable insights into the customs, art, religion and administrative capabilities of the occupants of Mohenjo-daro. The meticulously planned layout of this metropolis largely constructed with burnt bricks comprises significant features such as public baths, a priestly complex, an advanced drainage network, wells, soak pits for waste disposal and a substantial granary.
The remains of the ancient city were unknown for thousands of years. An Archaeological Survey of India (ASI) official, R D Banerji, exposed the site in 1920. It was later excavated in 1924–1926 and in the 1950s.
The fresh excavation continued for months in phases in 2025–26. The project was led by leading Pakistani archaeologists Asma Ibrahim and Ali Lashari along with Jonathan Mark Kenoyer of University of Wisconsin, Madison in the United States and a team of scholars and students from various universities from both countries.
“Pottery and carbon samples from the middle and upper levels of the new excavations confirm that the later phases of the mud-brick city wall at Mohenjo-daro were constructed during the Harappa Phase, beginning around 2600 BCE. The walls were expanded and maintained until around 2200 BCE and possibly even longer. Future investigations will trace the plan of the city wall around the Stupa Mound in order to try and locate gateways and to determine how this wall functioned and when it began to erode,” said DGAA.
The ancient settlement with a total population of 40,000 at its peak thrived for centuries before its abandonment around 1700 BCE.
Debate on urbanisation timeline
The findings have sparked a debate on whether the new discovery pushes Mohenjo-daro’s origins into the pre-urban phase - 3300 BCE.
Ahluwalia, also a columnist who regularly writes on the subject, said the findings still offer limited insight into the site’s origins but tell us about its developmental trajectory. The discovery of a rampart near the Stupa Mound suggests that earlier fortifications and settlement layouts differed from those of the mature urban phase, where defensive walls were built separately, Ahluwalia said.
“It does tell us about how cities grow, we still cannot tell much because the evidence is not yet very clear about the origin and of the site. It is just that there was an earlier settlement as well, which played an important role in the rise of urbanisation,” she said.
Ahluwalia rejected claims that the discovery pushes the timeline of urbanisation at Mohenjo-daro back to 3300 BCE. “We really cannot say that the urbanisation goes to 3300 because urbanisation is separate; what has been found is a pre-urban phase. It doesn’t push back the timeline of urbanisation nor do the excavators make the claim,” she added.
Additional Director General (ADG) of ASI Sanjay Kumar Manjul, however, said that the find could push back evidence of fortification and early urban traits by a few centuries.
“Traditionally, the Mature Harappan phase -- marked by large, well-built fortification walls -- is dated to around 2500 BCE. However, the discovery of a massive seven-to-eight-metre-thick wall in an earlier layer, dated roughly 2800-2600 BCE, is significant...The presence of Kot Dijian pottery beneath the structure strengthens this argument. This pottery belongs to the Early Harappan phase and has been dated to around 3000-3300 BCE at multiple sites. We have found similar material at Binjore near the India–Pakistan border, as well as at Rakhigarhi and other sites linked to the Saraswati basin,” he said.
Manjul has led or been part of the excavations at other significant sites of Indus Valley Civilization, such as Rakhigarhi (Haryana) and Binjore, near the International Border between Pakistan and India in Rajasthan.
These parallels indicate that the Indus Valley Civilization had earlier foundations than previously assumed, Manjul suggested. “We are now beginning to see clearer evidence of what may be called a ‘semi-urban’ or early urban phase emerging around 3000 BCE, preceding the fully developed urban phase,” he said. \On how this changes the understanding of Mohenjo-daro, he noted, “Earlier, fortifications at the site were associated primarily with the mature phase. Now, evidence of an earlier defensive structure suggests that organised planning and fortification began earlier than thought.”
He, however, cautioned against overstatement, which claims the ruins in Sindh could be the world’s earliest city.
“It started around 3000 BCE, a particularly fortified city. Parallelly, Saraswati Valley also started almost in 3000 BCE ...This discovery pushes back the timeline of urbanisation but we cannot say the oldest city, but certainly it's one of the oldest cities...At best, it may be regarded as one of the earliest urban centres but such assertions require stronger and more direct evidence.”
Mani also said that Mohenjo-daro is certainly an important city but it is not the only one. “Sites such as Harappa, Kalibangan and Rakhigarhi were also part of the same cultural horizon,” he said.
He explained that these urban centres evolved together across the broader Indus Valley Civilisation region. “While the beginnings of this process may go back to around 3200-3300 BCE or earlier, it was only by about 2700-2800 BCE that these settlements developed into large, mature urban centres. There was clear coexistence among them.” According to him, the entire Sindhu-Saraswati region, including the Indus system and the now dry Saraswati basin, witnessed this parallel development.