Astronomy arises very early in a civilisation and evolves as the civilisation advances. It is therefore reasonable to assume that a vibrant knowledge of astronomy would have been a feature of a civilisation the size of the Harappan Civilisation. We suggest that structures dedicated to astronomy existed in every major Harappan city. One such city was Dholavira, an important trading port that was located on an island in what is now the Rann of Kutch during the peak of the Harappan Civilisation. We have analysed an unusual structure at Dholavira that includes two circular rooms. Upon assuming strategically-placed holes in their ceilings we examine the internal movement of sunlight within these rooms and suggest that the larger structure of which they formed a part could have functioned as an astronomical observatory. 

Figure 3: Photograph of the Bailey structure at Dholavira.
Figure 3: Photograph of the Bailey structure at Dholavira. There are two circular rooms, one to the right of the picture and the other in the centre. The one on the right has a central structure that faces due North. .... As can be seen, the structure consists of rooms of circular and square shape. Since most other residential and workshop buildings in Dholavira are rectangular, it generally has been assumed that the Bailey structure also dates to the Late Harappan Period or an even later Period. However, we suggest that the Bailey structure dates to an earlier period, because of its unique combination of rectangular and circular rooms. Furthermore, we suggest that the two non-circular rooms were designed for non-residential purposes, because: 1) The rectangular rooms adjacent to the circular rooms had bathing and other utilitarian areas, but these were missing from the circular rooms. 2) Each rectangular room typically was connected to one or more other rooms, but each of the circular rooms had only one entrance. 3) Each of the circular rooms was far too small to have served as a residence. It also is clear that the Bailey structure was built on top of an earlier Harappan structure. We suggest that the entire Bailey area was infilled and reconstructed at the peak period of the city, thereby acquiring its present shape.