What events during the middle ages led to a growth of cities?

a historian researching the immigration policies of the early 1900s would expect a source written today,rather than in 1910 to :

( a ) be more interested in objective data and statistics.

- "the most famous structure by far at saqqara is djoser's step pyramid. dating from the 3rd dynasty (2667—2448 bc), it was the first all-stone complex ever built on earth."

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