for the sassanids, shahreevar has set you covered pretty well. But just to call some names off the top of my head, Ctesphion (later Baghdad) was the capital. Susa, Istakhr (later Shiraz), Takht-e Soleyman, Hamadan, Nineveh, Derbent, Ardashir-Khwarrah (AKA Gor AKA Firouzabad), Balkh, Bishapur...