It will be seen from the above that there was little in Arabia to attract the attention of the great powers of late antiquity, and at first it was only Arabia’s role athwart the route to the east that lent it any importance to them. This factor alone was sufficient to make Arabia a focus of imperial manoeuvring and power politics, but trade operated in conjunction with other factors as well. The spread of Christianity and to a lesser extent Judaism in Arabia reflects the interest of external powers from an early date. In fact, it was the great triad of politics, trade and religion that determined the course of events there from late antiquity onwards, with trade providing an imperial momentum later transferred to the other two factors. All around the peripheries of Arabia the impact of imperium was being felt. Behind the Roman presence advancing in the north came Roman roads, way-stations and forts, reflecting an increasing interest in control of what lay beyond. Far more vigorous, however, were the inroads by the Sasanians: they had a more immediate stake in Arabia, with their capital at Ctesiphon, the rich agricultural alluvium of Iraq, and the Persian Gulf trade to consider. Settlements were founded up and down the Gulf, and Oman was annexed by Shapur I (240–70). In the fourth century, Arab raids provoked a punitive expedition that reached as far as the Hijaz. Discovery of silver and copper in theNajd led to the foundation of a Sasanian outpost at Shamam.67 Several factors exacerbated the rivalry between the two imperial powers. The establishment under Constantine of a Christian empire based at Constantinople made competition with Persia more immediate and provided yet another arena for intrigue and dispute. But more important by far was the evolution of the rival polities themselves. From largely decentralised and culturally diverse empires, tolerant of a broad range of contradictory ideologies and traditions, both developed into world powers; they used political, economic and military strength to pursue imperial aims that were justified by elitist ideologies, spurred by aspirations to universal dominion, and increasingly dictated from the capital. The Byzantine and Sasanian empires competed for control of western Asia and adopted more global strategies in efforts to promote their own interests and undermine those of their rival.68 Thus, while the rise of Christianity led to the collapse of the market for the incense consumed so massively and ostentatiously by pagan Rome,69 the demise of this formerly crucial aspect of the eastern trade was more than replaced by new rivalries of unprecedented intensity. The new level of conflict generated by escalating competition between the two great powers manifested itself in several ways where Arabia and the Arabs were concerned. Firstly a pronounced religious element was introduced into the struggle, primarily in the southern part of the peninsula and surrounding lands. Monophysite missionary activity70 led to the conversion of Ethiopia to Christianity in the fourth century and the spread of the faith in Yemen and elsewhere in south Arabia. The Christian presence noted frequently in the Koran was probably the result of commercial contacts with Syria. The Sasanians, on the other hand, supported the spread of the rival confession of the Nestorians and also encouraged the Himyarites, a predominantly Jewish regime which ruled most of south Arabia and had influence elsewhere. Religious rivalries played an instrumental role in an Ethiopian invasion of Yemen in about 518 and shortly thereafter in a Himyarite civil war between Christian and Jewish factions. This struggle led to a persecution of Christians in south Arabia under the last Himyarite ruler Dhu Nuwas, culminating in the 520s with the massacre of the Christians of Najran. Ethiopia responded with a second invasion, killing Dhu Nuwas and once again installing a puppet regime in Yemen. The power of the Ethiopian governor, however, was soon usurped by a certain Abraha, who established himself as the paramount authority in the south; the Meccans viewed his expedition of 552 as directed against themselves, but it was in fact a move against tribal forces to the east. Secondly, external forces gradually encircled and penetrated the peninsula. The Sasanians established trading posts beyond the Straits ofHormuz as far as Aden and in the sixth century occupied Yemen. Persian authority extended as far as Yathrib, where taxes collected by the Jewish tribes of Qurayza and al-Nadir were sent on in part to a Persian ‘governor of the desert’ (marzub¯an al-b¯adiya).71 Byzantium, on the other hand, still had trade through Clysma and Ayla to protect,72 and sought a sea route to the east that would not be subject to Persian taxes and interference. It thus tried to extend its influence down the Red Sea and battled against pirates and adventurers to maintain control of ports and customs stations; epigraphical evidence places Byzantine forces nearly a thousand kilometres south of Damascus in the mid-sixth century.73 It also used its new Christian ally, Ethiopia, to pursue its economic interests and intervene militarily in the affairs of the south, encouraging the Himyarites to attack Persian interests.74 Thirdly, both powers used tribal allies in Arabia to further their own interests, protect their Arabian frontier zones, and confront the tribal forces of the other side. Such a tactic was not new. Rome and Persia had routinely used tribal auxiliaries in various capacities,75 and in the late fifth and early sixth centuries the Himyarites in Yemen coopted the great north Arabian tribal confederation of Kinda into acting in their interest and controlling caravan traffic along the routes from Yemen to Syria and Iraq. Kinda eventually extended its control across central Arabia, as well as part of the Hijaz and areas along the Persian Gulf coast, and in the early sixth century it was attacking both Byzantine and Sasanian targets along the desert fringes of Syria and Iraq. Seeking to avoid further incursions and to gain a strong tribal ally against forces acting for the Sasanians, the Byzantines reached an understanding with the confederation and on several occasions sent embassies to promote good relations. Kinda thus became an ally of Byzantium; turning against the Sasanians, it gained considerable authority in the hinterlands of south-western Iraq and even occupied al-Hira for a time.76 However, its primary sponsors remained the Himyarites in Yemen, and as this regime declined, so did the fortunes of Kinda. The Sasanians’ main tribal ally was the Lakhmids, a tribe that had established itself in north-eastern Arabia by the fourth century and founded a stable base at al-Hira. There had been contacts and relations between the two sides in the past, but the combination of deteriorating relations with Byzantium and the spectre of powerful Kinda forces allied to Byzantium and positioned within easy striking distance of Ctesiphon and the agricultural plains of Iraq led the Sasanians to support and encourage the Lakhmids with renewed vigour. The latter had long been subordinate to Kinda, and double marriages between them had been arranged at least twice in the past. Nevertheless, by about 504 the new Lakhmid chieftain, al-Mundhir III (504–54), was able to rid himself of Kinda suzerainty and launch operations against the confederation with a well-organised army.77 Fighting over the next two decades ended with the utter disintegration of Kinda and the extension of Lakhmid authority over their rival’s former clients among the Arab tribes. By the 540s the Lakhmids held sway over many of the tribes of central Arabia and over towns as far west as Mecca.78 Byzantium was thus forced to turn to other Arab clients for the protection of its position and interests. Its choice fell on the Ghassanids, a south Arabian tribe closely related to Kinda, that had migrated to northern Arabia and Syria in the fifth century and established itself as the pre-eminent power on the desert fringe there. The Ghassanids were a more nomadic group than the Lakhmids; although they were often associated with the camping-ground called al-Jabiya 65 kilometres south-west of Damascus, they had no real fixed centre comparable to that of the Lakhmids at al- Hira. Their influence was not as broad-ranging as that of the Lakhmids, and although they had trading connections with Iraq throughNisibis andDara, their control over the relevant routes was tenuous.Nevertheless, Byzantium granted the Ghassanid sheikh the title of phylarch and showered him with honours, privileges and money. In return, it was expected that the chieftain would keep his own tribe under control and protect imperial interests from other tribes as well.79 The Ghassanids and Lakhmids, confronting one another across the Syrian desert, were thus drawn into the series of great Byzantine–Persian wars that began in 502 and ended with a decisive Byzantine victory in 628 (see above, pp. 119–20, 124–7, 135–6). Significant fighting between them began in the 520s and continued sporadically for sixty years, with dire consequences for the agricultural infrastructure of both Syria and Iraq. Several observers describe the destruction in Syria,80 and whatever survived the passage of raiding parties and military expeditions was exposed to the brigands and outlaws hovering around such forces.81 This military conflict tends to overshadow other developments in which the two sides were variously involved. The Ghassanids were responsible for the establishment of several small towns in the hinterlands south of Damascus and perhaps also for some of the so-called ‘desert palaces’ of the Syrian steppe.82 Sponsors of monophysite Christianity, they also erected numerous churches and monasteries. In Iraq, al-Hira grew from a camp (which is what the name means in Arabic) into a lively Arab town, noted for its churches and monasteries, impressive residential compounds and taverns. Persian Gulf shipping could sail up the Euphrates as far as al-Hira, and Lakhmid income included proceeds not only from raids but also from agricultural rents and produce, trade, and taxes from tribes they controlled. There also seems to have been a nascent literary tradition emerging there.83 Both sides, especially the Lakhmids, were also major patrons of Arab oral culture, and some of the most important poets of pre-Islamic times gained generous support from Ghassanid or Lakhmid sheikhs.84 The history of the Arab client regimes is important, but they were not central in the imperial planning of either Byzantium or Persia, in which they figured mainly as threats that had to be countered.85 Little is knownfromthe Lakhmid and Persian side, but Byzantine emperors, political strategists and historians such as Procopius certainly held the Ghassanids in low esteem. The Byzantines had little faith in the abilities, motives or intentions of their Arab allies. The treaty of 561, for example, expresses dissatisfaction with Saracen adherence to treaty terms in the past, comes close to calling them smugglers and traitors, and warns of harsh punishment for lawbreakers.86 When Ghassanid phylarchs refused to adhere to Chalcedonian orthodoxy, they were exiled. Byzantium made overtures to the Lakhmids when it was expedient, and the lack of trust and commitment worked both ways: the capture of Dara by Khusro I probably involved some negotiations with the Ghassanid phylarch al-Mundhir (569–82).87 Neither side survived the manoeuvrings of their patrons or the broader conflict which engulfed the Middle East in the sixth century. In 581 al- Mundhir was arrested by Emperor Tiberius I (578–82) and exiled to Sicily in a religious dispute, and in 584 his son and successor al-Nu‘man joined him. The Ghassanid phylarchate rapidly fell apart, fragmented by Emperor Maurice (582–602) into a host of smaller entities and riven with dissension and conflict over the deposition of two leaders within four years. Forces from the tribe are mentioned in accounts of the Arab conquest of Syria, but not in a leading role.88 The Lakhmids survived a while longer, but during the reign of Shah Khusro II (591–628) they were displaced in favour of a similarly decentralised system. The Sasanians also promoted the position of the Banu Hanifa, who roamed in the desert on their southern flank.89 Later, when a force of Persian troops and Arab auxiliaries sought to quell a desert revolt in about 610, their army was beaten at Dhu Qar; this was the first time the tribes had been able to defeat the Sasanians in battle.90 It also illustrates how the demise of the Arab client regimes marked not the shift from one system of frontier defence to another, but rather the opening of a great power vacuum extending from the desert fringes of Syria and Iraq all the way to central Arabia. Inhabitants of the peninsula remembered that they had once been ‘trapped on top of a rock between the two lions, Persia and Byzantium’.91 But as the next decade was to reveal, those days were gone forever and the Persian setback at Dhu Qar was but a hint of things to come.