The emergence of the unified monarchy of León-Castile in the twelfth and thirteenth centuries is perhaps one of the most significant developments in the history of Iberia, and one which was to have long-lasting consequences for the religious, political, and cultural configuration of the Iberian peninsula. While traditional Spanish (national) historiography has tended to depict this political development as an inevitable reemergence of a “united Spain” following the rupture inaugurated by the Muslim conquest, more recent scholarship has tended to be wary of such an essentializing approach in which there is institutional and ideological continuity drawn between the Visigothic monarchy and the Christian kingdoms of northern Iberia. Rather than viewing the emergence of the kingdom of León-Castile as a natural political evolution, modern historians have emphasized the importance of the Muslim-Christian frontier in Iberia and the process of Christian conquest and settlement, known as the Reconquista, at the expense of al-Andalus (Muslim-ruled Iberia) as central to the rise of the Christian kingdoms of northern Spain between the tenth and twelfth centuries.
The question of the Roman-Byzantine desert frontier in Late Antiquity has attracted the attention of various scholars in the past several decades. This frontier, known as the LimesArabicus, spanned more than 1,300 kilometers from northern Syria to southern Palestine and the edges of the Arabian Peninsula. Recent research and excavations have done much to augment scholarly knowledge of this frontier, which served as the south-eastern defense of the Roman Empire for over six centuries, until it was eventually overrun by the Arab Muslim conquerors in the 630s. This frontier consisted not only—nor even primarily—of fortifications and watchtowers, but also of major nomadic tribal confederations, allied to Rome, which patrolled the desert and ensured the security of the eastern provinces by exercising control over nomadic movements both within and, to a certain degree, beyond the boundaries of the Roman Empire. Although much attention in recent years has been devoted to the Ghassānids, which served as a major tribal confederation allied to Rome well into the seventh century, the fourth century has been relatively less discussed. Those scholars, including Irfan Shahid, Greg Fisher and Glen Bowerstock, who have devoted their scholarship to understanding this period have indicated its importance and have sought to underscore that the fourth century witnessed both the rise of major Arab tribal confederations along the desert frontier and the establishment of Roman foedus agreements, or alliances, with them.