This article highlights the significant role played by Constantia, posthumous daughter of the emperor Constantius II, in late fourth century dynastic politics and ideology. Though Constantia has generally been neglected in modern studies of the period, close examination of the surviving sources reveals her pivotal position, even from her earliest years, as a coveted link between the Constantinian dynasty and new emperors seeking to establish themselves and their families in the turbulent years of the 360s, 370s and 380s AD. Through investigation of the source material relating to Constantia's short life, we gain further vital insight into the perennial importance to imperial politics of dynastic loyalty, and specifically loyalty to the Constantinian house, in the late fourth century, as well as emerging new ideas about the complexities of the marriages of imperial women.