Valentinian I, upon becoming emperor of the Roman Empire, recognized the need for a reliable and competent partner to help manage the vast territories and the mounting challenges faced by the empire. In a crucial ceremony at Nicaea, he appointed his younger brother Flavius Valens as co-emperor. Valens had a military background, having served successfully in various campaigns, and his appointment was expected to bring stability and effective governance to the Eastern provinces of the empire, which faced increasing pressure from external enemies, particularly the Sassanid Persians.

The co-emperorship represented a significant political strategy, reflecting a division of responsibilities. While Valentinian would govern the Western regions, Valens would be in charge of the Eastern territories, where threats from Persia and internal dissent were particularly acute. This joint leadership aimed to maintain peace and order in the empire, which was vital for its survival during a period marked by political strife and military peril. Valens' governance was characterized by a focus on consolidating power and stabilizing eastern provinces, which were experiencing significant challenges, including religious conflicts and Persian incursions.

Moreover, the establishment of co-emperorship contributed to the later developments within the Roman political system, as it set a precedent for future emperors to appoint successors or share power, leading to a more intricate governmental structure. The alliance between the two brothers was also rooted in familial loyalty and the desire to uphold the dynasty, reinforcing the importance of blood relations in the political landscape of the time.