Scholars are unable to draw a conclusion regarding the religion of Indus people. Unlike Mesopotamia or Egypt, there was no such buildings discovered so that we can conclude it might be a temple or involve any kind of public worship. However some historians are of the opinion that Harappan people were Hindus.
The Harappan religion was polytheistic. They used cattle, elephants and other animals to represent their Gods. The Harappan seals were amulets addressed to the Harappan Gods. The Gods of the Harappans depicted on their seals represented the Gods of the various economic corporations in the Indus Valley. The unicorn God, probably represented `Ma`, while the cattle God probably represented Kali or Uma, Amma or Pravarti, the mother goddess.
The bulk of public buildings in the city seemed to be solely oriented towards the economy and making life comfortable for the Harappans. We do, however, have a number of tantalizing figures on various seals and statues. What we gather from these figures, is that the Harappans probably exercised some sort of goddess worship. There is, however, some sort of male god that has the head of a man with the horns of a bull. In addition, we believe from various artifacts that the Harappans also may have worshipped natural objects or animistic forces, but the circumstances of this worship can only be guessed at.
No temple has yet been discovered. From the Pashupati seal, it is certain that they worshipped Shiva. There is an image of Shiva, seated on a stool flanked by an elephant. Numerous pottery figurines of Mother Goddesses have also been found. Nature worship must have been part of their ritual as revealed in the seals. There is a scene of a horned goddess, before whom another horned deity is kneeling and animals as some male figures wearing the horns of a goat or a bull, some animals standing on rectangular pedestals, composite animals having body of a ram and trunk of an elephant, a limestone bull having a garland round his neck and a unicorn being carried in a procession.
However Historian John Keays in his book on Religion of Harappans countered this view. He states:
"The religion of Harappans is unknown. No site has certainly been identified as a temple and most suppositions about sacrificial fires, cult objects and deities rest on doubtful retrospective references from Hindu practices of many centuries later. Such inferences may be as futile as, say, looking to Islamic astronomy for an explanation of the orientation of the pyramids. In short, these theories are all fanciful and do not bear scrutiny".
"Depicted on some Harappan seals, is that of a big-nosed gentleman wearing a horned head-dress who sits in the lotus position, an air of abstraction and an audience of animals. He cannot be the early manifestation of Lord Shiva as Pashupati, `Lord of the Beasts.` Myth, as has been noted, is subject to frequent revision. The chances of a deity remaining closely associated with the specific powers - in this case, fertility, asceticism, and familiarity with the animal kingdom - for all of two thousand years must raise serious doubts, especially since, during the interval, there is little evidence for the currency of this myth. Rudra, a Vedic deity later identified with Shiva, is indeed referred to as Pasupati because of his association with the cattle, but asceticism and meditation were not Rudra`s specialties nor is he usually credited with an empathy for animals other than kine. More plausibly, it has been suggested that the Harappan figure`s heavily horned headgear bespeaks a bull cult, to which numerous other representations of bulls lend substance.
"Similar doubts surround the female terracotta figurines which are often described as mother goddesses. Pop-eyed, bat-eared, belted and sometime miniskirted, they are usually of crude workmanship and grotesque mien. Only a dusty-eyed archaeologist could describe them as `pleasing little things.` The bat-ears, on closer inspection, appear to be elaborate head dresses or hairstyles. If, as the prominent and clumsily applied breasts suggest, they were fertility symbols, why bother with millinery? Or indeed miniskirts?"
"Similar to the cultures of ancient Middle East, it appears that the Indus religion recognized some type of life after death. Unlike Hindus who practice cremation, Indus people carefully buried their dead in wooded coffins with their heads facing north and the feet pointing south. Included in the graves were pottery jars containing food and weapons for use in the afterlife."
Science and Astronomy:
The Harappan people knew the measuring tools of length, mass, and time. They were the first in the world in developing a system of uniform weights and measures. Their measurements were extremely precise. Their smallest division, which was marked on an ivory scale found in Lothal, was approximately 1.704mm, the smallest division ever recorded on a scale of the Bronze Age. They also followed the decimal division of measurement for all practical purposes, including the measurement of mass as revealed by their hexahedron weights.
Brick sizes were in a perfect ratio of 4:2:1, and the decimal system was used. Weights were based on units of 0.05, 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 50, 100, 200, and 500, with each unit weighing approximately 28 grams. In addition, they evolved new techniques in metallurgy, and produced copper, bronze, lead, and tin. The engineering skill of the Harappans was remarkable, especially in building docks after a careful study of tides, waves, and currents.
The Harappans were well versed in astronomy. It is clearly evident from the excavations. The straight streets of the Indus cities were oriented towards the basic directions, which presupposes astronomical observations and the use of the sun-stick. The Aryans in India adopted the star-calendar used by the Vedic ritualists. But there are no references to it in the Avesta or in the oldest books of the Rigveda. On the other hand, astronomical evidence dates the compilation of this calendar at around the 23rd century B.C., when the Indus civilisation flourished at its peak. Linkages between ancient Harappan scripts and latter Vedic texts suggest that Harappan priest-astronomers tracked progress of Mercury, Venus and Saturn, and most likely all of the planets.