Definition of eternal city:
(n) :
Nickname for Rome: the capital of Italy.
(n) :
Nickname for Jerusalem: a city in West Asia; the claimed capital cities of Israel and Palestine.
(n) :
(historical) Former nickname for Kyoto: a major city in Japan, during the period when it was named Heian-kyō and served as the capital of Japan; c. 800–1000 CE.