Short answers, pulled from the story.
Mithridates I of Parthia established a military camp across from Seleucia in the late 120s BC. This small outpost grew into Ctesiphon, which eventually spanned thirty square kilometers.
Ctesiphon officially became the Empire's capital by circa 58 BC under Orodes II. The settlement reached its first peak as a political and commercial hub during the reign of Gotarzes I before this transition.
Muslim Arabs occupied Ctesiphon in early 637 AD after defeating the Sasanian Empire at the Battle of al-Qādisiyyah. By the end of the eighth century, the site became a ghost town after Caliph Al-Mansur used materials from the ruins to construct Baghdad starting in the 760s.
Oscar Reuther led a German Oriental Society expedition that excavated at Ctesiphon between 1928 and 1929. Winter seasons from 1931 to 1932 saw joint efforts by the German State Museums and The Metropolitan Museum of Art, while an Italian team from the University of Turin worked on the opposite side of the Tigris during the late 1960s and early 1970s.