But, on the material side, the greatest change they effected in the life of Babylonia was due to their introduction of the horse. There can be little doubt that they were a horse-keeping race,[1] and the success of their invasion may in large part be traced to their greater mobility. Hitherto asses and cattle had been employed for all purposes of draught and carriage, but, with the appearance of the Kassites, the horse suddenly becomes the beast of burden throughout Western Asia. Before their time "the ass of the mountain," as it was designated in Babylonia, was a great rarity, the earliest reference to it occurring in the age of Hammurabi.[2] In that period we have evidence that Kassite tribes were already forming settlements in the western districts of Elam, and when from time to time small parties of them made their way into the Babylonian plain to be employed as harvesters,[3] they doubtless carried their goods with them in the usual way. The usefulness of horses imported in this manner would have ensured their ready sale to the Babylonians, who probably retained the services of their owners to tend the strange animals. But the early Kassite immigrants must have been men of a simple and unprogressive type, for in all the contract-literature of the period we find no trace of their acquiring wealth, or engaging in the commercial activities of their adopted country. The only evidence of their employment in other than a menial capacity is supplied by a contract of Ammi-ditana's reign, which records a two-years' lease of an uncultivated field taken by a Kassite for farming.[4]