In the 1923-24 season, Trench A(b) was one of the extensions dug by Daya Ram Sahni from the centre of Trench A in Mound F. Sahni describes the parallel walls in his report of the season's excavations.
Ancient Indus walls.
A massive baked brick revetment wall  surrounds the solid mud-brick foundation platform  of the "granary" that measures approximately 51 meters north-south and 41 meters east-west.
Overview looking north of excavations at the southeast corner of the "granary" structure undertaken in 1999 (Trench 1C). The higher east-west running walls in the left of the image and the ruined structures in the right of the image all post-date
After clearing the overlying silt, the original forms of the baked brick walls and hollow buttresses of the "granary" could be made out.
Individual rooms are 15 by 6 meters long, and have sleeper walls for airspace between them. At each end of the rooms are three raised platforms.
The high mound at Harappa (Mound AB) is surrounded by a massive mud brick city wall with large square ramparts. One of these eroding ramparts is visible through the underbrush that now covers the site.
Eastern Wall – Remnant of the eastern wall after the fortification of the city. There are gates on the wall running along its periphery.
Deep digging at the southeast corner of the "granary" revealed an earlier building [wall 330] constructed along the same east-west alignment. This structure could have been built as early as the beginning of Period 3B, ca. 2450 BC.
One relatively successful low cost techniques used to combat the destructive nature of salts in the fired bricks is to cover the walls with a thick layer of mud and straw plaster and to spray them with clay slurry.