Mysteries, or open questions?
Much about the Indus Valley civilization is known, including how its cities were built, what its people ate and how its crafts were made. What remains unclear are questions the physical remains cannot easily answer, such as what language people spoke, who ruled, and what they believed. These are open questions rather than mysteries without clues, and for each one there is evidence and more than one reasonable reading. The sections below set out the main ones.
What language did the Harappans speak?
The language is unknown. Candidates include an early Dravidian language, an early Indo-Aryan language, a Munda (Austroasiatic) language, or one that left no later trace. Arguments rest on small pieces of evidence. Brahui, a Dravidian language, is still spoken in Balochistan, and Dravidian features appear in the earliest Indo-Aryan texts, which some scholars read as hints of an older Dravidian presence. Others point to Vedic loanwords and place names. Without a deciphered script or any long text, none of this can be tested decisively. The script has so far resisted every attempt, and the Indus script debate shows no sign of ending. Evidence about people’s ancestry does not by itself answer a question about language.
Who ruled?
In Mesopotamia, kings and temples left monuments, inscriptions and rich tombs, and a state with a clear hierarchy is visible. In the Indus cities, no palace has been identified with confidence, and royal burials, large statues of rulers and war scenes are absent. Compared with the Sumerian city-state kingship known from contemporary Mesopotamia, the Indus evidence is much harder to read.
Interpretations vary. A statue from Mohenjo-Daro, nicknamed the “Priest-King”, has been cited as evidence of a ruling priest, but the name was given by early excavators and rests on assumption. Some scholars suggest rule by city councils or merchant groups, others a centralised state, and others a looser network of cities sharing customs. The standard weights and bricks are used as evidence for central control, but they could equally result from agreement among traders. The question is unresolved.
What did they believe?
Without readable texts, religion has to be inferred from objects. Female terracotta figurines have been called “mother goddess” figures, though it is not clear they were all deities. A seal showing a seated figure with horns, surrounded by animals, has been called a proto-Shiva or “Pashupati” figure, and some scholars see links to later Indian religion, while others consider this a projection of later beliefs onto an unlabelled image. Fire altars were claimed at places such as Kalibangan, and the identification is debated. The Great Bath of Mohenjo-Daro may have been used for ritual washing, but this is an inference from its design. Trees, bulls and composite animals appear on seals, which suggests symbolic importance without telling us the meaning.
Why such elaborate drains?
Indus cities are known for drains, often brick-lined and covered, running from houses to street channels, and for private bathing areas and numerous wells. Their purpose is debated. The simplest reading is hygiene and waste removal. Others suggest concern with ritual purity, status display or flood and rainwater management. Some drains had inspection chambers and sumps for cleaning, which implies maintenance, though by whom is unknown. Not all houses or cities had the same facilities, and some drains may have emptied into soakage pits instead of going to rivers. Drainage thus points to organisation, but not to a clear motive.
How were people buried, and how many were there?
Burials are surprisingly few relative to the size of the cities. Cemeteries at Harappa and elsewhere contain bodies, often with pots and some jewellery, but many people are not accounted for, which raises the question of what happened to the rest. Possible answers include cremation, disposal in rivers, or burials not yet found. This makes population estimates uncertain. Figures for the largest cities range from several thousand to tens of thousands, depending on assumptions about house sizes and unexcavated areas.
Why did the cities decline?
The end of the urban phase is a major open question. Climate change, shifting rivers, changing trade and local pressures are all proposed, and none by itself explains everything. The invasion explanation once popular is no longer supported. Evidence comes from sediment cores, river deposits, pottery sequences and settlement surveys, each with limits. Specialists tend to combine several factors, and different regions probably changed at different speeds, so there may never be one answer, and Indus decline theories differ mainly in which factors they stress.
Relationship with later India
Another question is how far Harappan traditions continued into later South Asian societies. Craft techniques, symbols, and some religious motifs may have survived, but such continuities are hard to prove. Genetic studies, including ancient DNA from Rakhigarhi, show that the people of the Indus cities contributed to later populations, though they do not resolve questions of language or culture.
Why uncertainty is part of the picture
Many questions persist because only a small part of each city has been excavated, early digs were not recorded to modern standards, and writing remains unread. New methods, new finds and re-study of old collections can change the picture, so statements about the Harappans are best held with care.