Patras is Greece's third-largest city and the regional capital and largest city of Western Greece, in the northern Peloponnese, 215 km west of Ath…Patras is Greece's third-largest city and the regional capital and largest city of Western Greece, in the northern Peloponnese, 215 km west of Athens. The city is built at the foot of Mount Panachaikon, overlooking the Gulf of Patras.