From a Roman perspective the Arabian Peninsula was frequently relegated to a peripheral position on the edge of the empire. In contrast, in different stages of Sasanian history the Arabian frontier acted as a keystone of their empire. Sasanian control, both direct and indirect, of the Arabian Peninsula strengthened its economic prosperity and military security. It was for these reasons that the empire's activities on their southern frontier in Arabia peaked during three distinct periods: during the early Sasanian period, principally in the reigns of Ardashir I and Shapur I; during the reign of Shapur II; and, perhaps most importantly, during the sixth century in renewed hostilities with the Roman Empire.

As Warwick Ball, Dan Lawrence, Tony Wilkinson and Kristen Hopper have analysed the nature and importance of the Sasanian Empire's northern, western and eastern frontiers elsewhere in this volume, it is now time to turn our attention to the empire's southern frontier in Arabia. From a western, Roman-centric perspective the Arabian Peninsula has often been regarded as an insignificant periphery of the ancient world; however, for the Persians it was arguably of much more central importance. The geopolitical position the Sasanians found themselves in after overthrowing the Parthians in 224 necessitated close relations with Arab tribes and a degree of authority over the Arabian Peninsula.1 Indeed, from the foundation of the Sasanian Empire Arabia played a significant role in its security and economic prosperity. As such, it will be argued here that the southern frontier in Arabia was a keystone of the Sasanian Empire at various points throughout its history. In understanding the important role the southern frontier fulfilled this chapter will have two main areas of focus. First, it will be necessary to show at what points in Sasanian history it acted as a keystone of empire. Secondly, an attempt will be made to show why Arabia was important and what strategies the shahs employed to ensure their control of the region.

It is important to stress that Sasanian activity and involvement in Arabia fluctuated over time in response to developments on the southern frontier itself and also to events elsewhere in the empire. Fortunately, there is both literary and archaeological evidence which allows us to trace the development of Sasanian activity on the southern frontier.