Apart from the tablets of the Kassite period discovered at Nippur,[62] our principal source of information on economic conditions in Babylonia at this time is to be found in the kudurru-inscriptions, or boundary-stones, to which reference has already been made.[63] The word _kudurru_ may be rendered accurately enough as "boundary-stone," for the texts are engraved on conical blocks or boulders of stone; and there is little doubt that many of the earlier stones must have been set up on landed estates, whose limits and ownership they were intended to define and commemorate. Even at a time when the stone itself had ceased to be employed to mark the boundary and was preserved in the owner's house, or in the temple of his god, as a charter or title-deed to which he could appeal in case of need, the text preserved its old formulas setting out the limits and orientation of the plot of land to which it referred. The importance of these records is considerable, not only in their legal and religious aspects, but also from a historical point of view. Apart from the references to Babylonian kings and to historical events, which they contain, they form in many cases the only documents of their period which have come down to us. They thus serve to bridge the gap in our knowledge of Euphratean civilization between the Kassite epoch and that of the Neo-Babylonian kings; and, while they illustrate the development which gradually took place in Babylonian law and custom, they prove the continuity of culture during times of great political change.[64]