Special feature about Harappan cities: Many of these cities were divided into two or more parts. Usually, the part to the west was smaller but higher and is called the citadel. Generally, the part to the east was larger but lower and is called the lower town. Very often walls of baked brick were built around each part. The bricks were laid in an interlocking pattern and that made the walls strong. In some cities, special buildings were constructed on the citadel. For example, in Mohenjodaro, a very special tank called the Great Bath, was built in this area. Other cities, such as Kalibangan and Lothal had fire altars, where sacrifices may have been performed.