Final answer:
The Indus Valley cities were characterized by fortified citadels that served as a ceremonial center and possibly hosted religious activities. Unlike other ancient civilizations, the cities lacked palaces and instead focused on advanced urban planning and infrastructure.
Step-by-step explanation:
Each city in the Indus Valley civilization was surrounded by walls and had a number of distinct features in addition to the grid patterns. The most significant of these features was a fortified citadel area, which was part of every city. These citadels contained public areas such as baths and might have served as monumental ceremonial centers for ritual activities, likely also hosted the residences of the ruling elites or religious specialists. There is evidence that suggests the citadels were used for religious purposes. Apart from the fortified citadels, these cities were also characterized by their advanced urban planning, including orderly streets and advanced drainage systems, unlike the grand palaces that one might associate with other ancient civilizations. Unlike a ziggurat or pyramid, which might serve as a ceremonial center in other ancient cultures, the citadel served this purpose within the Indus Valley cities.