The overall gateway structure, including the street and side drains is bonded at either edge (east and west) by massive mud brick bastions, representing the Mound E and Mound ET perimeter walls. The area between these two mud brick perimeter walls was apparently filled with smaller structures, now destroyed. The baked brick gateway is built on top of a mud brick foundation on the west and an earlier mud brick wall on the east. The width of these mud brick structures and baked brick gateway ranges from two to three meters. At least three major rebuilding phases can be identified for this structure. These rebuilding phases appear to be correlative with the three rebuilding phases of the construction, reconstruction, and repair of the Mound E perimeter wall.
The central corbeled arch drain is open at both the north and south ends and may have been a culvert beneath a street running east-west just inside the gateway and perimeter walls. The drain is set into horizontally laid layers of gravely deposits characteristic of streets. The drain is approximately 2 meters high by 1.5 meters wide with a length of approximately 5 meters. The drain interior is formed by a corbel arch built over a rectangular channel. Approximately 1.2 meters of street deposits were eventually laid down over the top of the drain during its final period of street use. A smaller unlined drain (excavated into the natural soil) continues to the south and would serve to carry rainwater and debris farther outside the ancient city. This unlined drain appears to have limited traffic through the gateway to that on foot. An older, unlined drain appears to have been carved below the level of this drain and apparently carried sewage waste (as indicated by the greenish stain associated with the deposits).
Directly to the west of the western pier and set into the baked brick wall is what appears to be side drains. These three drains superimposed on each other and may have been used for sewage disposal as indicated by the-green-stained deposits. The earliest two drains have been constructed on top of each other above the western edge of the gateway pier. These drains are identical in shape and size. These drains have floors constructed of baked bricks and slots apparently for wooden beams. These wooden beams could have comprised a moveable gate or grate. The third and latest drain is offset from the two previous drains and was constructed with a corbel arch with no slots for wooden beams.
This reconstruction was completed and rendered in MicroStation. It should be noted that the computer generated graphics represent the top and bottom of each individual wall as an idealized planar structure and not the detailed topography of the individual surfaces. In general, structures built on top of earlier structures were constructed on surfaces planned off by the Harappans. Most of the measurements are from HARP notebooks and were not measured off sections and plan. While individual elevations of various archaeological features and structures may vary by several tens of centimeters over the entire site (where they can be traced across large areas), most elevations within relatively small areas (such as the gateway area) do not vary over more than a few centimeters.