Boundary stones -- kudurru monuments -- were used in the Kassite and succeeding eras as permanent records of land ownership and of privileges such as tax exemptions. They generally describe sales or royal grants or judgments. Sometimes they confirm disputed decisions made by previous kings. They are among the most important sources for understanding Kassite administration and society. The sun, moon and star at the top of a boundary stone symbolize Shamash, Sin and Ishtar. As major Mesopotamian sky-gods, they witness and guarantee the legality of the boundary stones. Additional symbols refer to other gods and celestial powers, including precursors of the zodiac signs.