In the 2nd century CE, the balance of power shifted emphatically in favour of the Romans. A series of invasions repeatedly overran Mesopotamia and sacked the Parthian capital of Ctesiphon, made substantial territorial gains in northern Mesopotamia and benefited from the manipulation of frequent Parthian dynastic civil wars, which eventually undermined the Parthian state. Under Caracalla, an interesting twist in Parthian relations occurred. After submitting a request to marry the daughter of Persian king Artabanus V (potentially allowing an heir to assume control of both empires) Caracalla massacred the diplomatic party sent to arrange the marriage and attempted an invasion of Persia in 216. This was eventually unsuccessful and the Persians soon retaliated, inflicting heavy losses upon the Romans.