About the beginning of the third century after Christ a number of Bedouin tribes, wholly or partly of Yemenite origin, who had formed a confederacy and called themselves collectively Tanúkh, took advantage of the disorder then prevailing in the Arsacid Empire to invade ‘Iráq (Babylonia) and plant their settlements in the fertile country west of the Euphrates. While part of the intruders continued to lead a nomad life, others engaged in agriculture, and in course of time villages and towns grew up. The most important of these was Ḥíra (properly, al-Ḥíra, _i.e._, the Camp), which occupied a favourable and healthy situation a few miles to the south of Kúfa, in the neighbourhood of ancient Babylon.[84] According to Hishám b. Muḥammad al-Kalbí († 819 or 821 A.D.), an excellent authority for the history of the Pre-islamic period, the inhabitants of Ḥíra during the reign of Ardashír Bábakán, the first Sásánian king of Persia (226-241 A.D.), consisted of three classes, viz.:-- (1) The _Tanúkh_, who dwelt west of the Euphrates between Ḥíra and Anbár in tents of camel's hair. (2) The _‘Ibád_, who lived in houses in Ḥíra. (3) The _Aḥláf_ (Clients), who did not belong to either of the above-mentioned classes, but attached themselves to the people of Ḥíra and lived among them--blood-guilty fugitives pursued by the vengeance of their own kin, or needy emigrants seeking to mend their fortunes. [Sidenote: The ‘Ibád.] Naturally the townsmen proper formed by far the most influential element in the population. Hishám, as we have seen, calls them 'the ‘Ibád.' His use of this term, however, is not strictly accurate. The ‘Ibád are exclusively the _Christian Arabs of Ḥíra_, and are so called in virtue of their Christianity; the pagan Arabs, who at the time when Ḥíra was founded and for long afterwards constituted the bulk of the citizens, were never comprised in a designation which expresses the very opposite of paganism. _‘Ibád_ means 'servants,' _i.e._, those who serve God or Christ. It cannot be determined at what epoch the name was first used to distinguish the religious community, composed of members of different tribes, which was dominant in Ḥíra during the sixth century. Dates are comparatively of little importance; what is really remarkable is the existence in Pre-islamic times of an Arabian community that was not based on blood-relationship or descent from a common ancestor, but on a spiritual principle, namely, the profession of a common faith. The religion and culture of the ‘Ibád were conveyed by various channels to the inmost recesses of the peninsula, as will be shown more fully in a subsequent chapter. They were the schoolmasters of the heathen Arabs, who could seldom read or write, and who, it must be owned, so far from desiring to receive instruction, rather gloried in their ignorance of accomplishments which they regarded as servile. Nevertheless, the best minds among the Bedouins were irresistibly attracted to Ḥíra.