This idiom means "said to herself" or "she thought." The city is spoken of as if it were a person that could speak. It represents the people who live in that city. (See: [[rc://en/ta/man/translate/figs-idiom]] and [[rc://en/ta/man/translate/figs-personification]] and [[rc://en/ta/man/translate/figs-metonymy]])
It may be necessary to supply an object for "I am." Alternate translation: "I am the greatest city, and no other city is equal to me" (See: [[rc://en/ta/man/translate/figs-explicit]])