How do we know about ancient cultures and why do we refer to these as “civilisation” when the concept of “civil” is modern?

The resident of a city, in Latin, from ancient Rome, is a “civis”. Hence, the word “civil”, itself, dates from ancient times. The concept of “civil” is more or less the same as it was in ancient times — behavior suitable for a complex, urban society, in which law and social norms are required to regulate the behavior of “citizens”. We know about ancient cultures mainly, and especially, from ancient texts in Greek, Latin, Chinese, Egyptian hieroglyphics, and ancient Sumerian clay tablets. https://www.quora.com/How-do-we-know-about-ancient-cultures-and-why-do-we-refer-to-these-as-civilisation-when-the-concept-of-civil-is-modern