The architecture of Western Asia is greatly influenced from the beginning to the end by having not enough stone and wood and lots and lots of clay .
Buildings tend to be built of brick, or mud-brick, if at all possible.
Even buildings which are built of stone may look like they are made of brick. All of these people were used to living and entertaining in tents, and they built their houses and palaces kindof like tents, so they would feel at home. They also built city walls out of bricks. The Assyrians did not build ziggurats anymore, but they built themselves great palaces out of limestone . And city walls, still out of bricks.