Ctesiphon was undoubtedly one of them.

All writers agree that it was the chief city of the Empire, and the ordinary seat of the government.

Here, according to Strabo, the kings passed the winter months, delighting in the excellence of the air.

The town was situated on the left bank of the Tigris, opposite to Seleucia, twelve or thirteen miles below the modern Baghdad.

Pliny says that it was built by the Parthians in order to reduce Seleucia to insignificance, and that when it failed of its purpose they built another city.
Vologesocerta, in the same neighborhood with the same object; but the account of Strabo is more probable--viz., that it grew up gradually out of the wish of the Parthian kings to spare Seleucia the unpleasantness of having the rude soldiery, which followed the Court from place to place, quartered upon them The remainder of the year, Strabo tells us, was spent by the Parthian kings either at the Median city of Ecbatana, which is the modern Hamadan, or in the province of Hyrca--In Hyrcania, the palace, according to him, was at Tape and between this place and Ecbatana he no doubt regarded the monarchs as spending the time which was not passed at Ctesiphon.