Final answer:
The Harappa and Mohenjo-Daro civilizations were two important urban centers of the Indus Valley civilization. Harappa likely came first, followed by Mohenjo-Daro. Both cities had similar structures and may have had some form of central authority. They flourished from around 2600 to 1900 BCE and influenced later Indian civilizations.
Step-by-step explanation:
The Harappa and Mohenjo-Daro civilizations were two important urban centers of the Indus Valley civilization. While the exact relationship between the two civilizations is still being studied, it is believed that Harappa came first, followed by Mohenjo-Daro.
Both cities had similar structural organizations, with well-laid-out city streets and advanced drainage systems. This suggests the presence of some form of central authority.
Overall, the Harappa and Mohenjo-Daro civilizations flourished around 2600 to 1900 BCE, and they left a lasting impact on later Indian civilizations.