The Daylamites or Dailamites were an Iranian people inhabiting the mountainous regions of northern Iran. They were employed as soldiers from the time of the Sasanian Empire, and long resisted the Muslim conquest of Persia and subsequent Islamization.
Ctesiphon - capital of empire
The imperial capital of the Sasanian Empire, Ctesiphon and its environs were among the largest urban sites in the late antiquity. It became the capital and the winter residence of the Parthian kings.