Final answer:
The monumental ceremonial center in Indus valley cities was likely the citadel. It served as a ritual center for religious activities and the residence of the ruling elite.
Step-by-step explanation:
In the Indus valley cities, the monumental ceremonial center was likely the citadel. The citadel served as a ritual center for religious activities and also functioned as the residence of the ruling elite. Similar to palaces and temples in Egypt and Mesopotamia, the citadel was a walled-off area within the city, and it had platforms where ritual activities took place. It was a symbol of power and authority.