Sentence Correction

EducationAisle wrote:

chendawg wrote: Regarding your question, the second part isn't an independent clause. If it were then we'd need a semicolon.

Nops; flourished is a proper verb here. However, the second part (the site of....) is not an Independent clause; just a appositive modifier comprising a phrase the site of an ancient civilization + a dependent clause that flourished at the same time as the civilizations in the Nile delta and the river valleys of Tigris and Euphrates

Edit: Just thought simpler similar example might help understanding:

He is Sachin, the player who has scored maximum centuries for the country.

the player who has scored maximum centuries for the country is an appositive modifying Sachin and this sentence (as is perhaps easier to see) is not a run-on sentence.