It is quite possible that, when Nabû's temple-tower is excavated, it will throw some light upon the upper structure of these massive buildings. Meanwhile we possess a piece of evidence which should not be ignored in any discussion of the subject. On a boundary-stone of the time of Merodach-baladan I. are carved a number of emblems of the gods, including those of Marduk and Nabii, which are set beside each other in the second row. That of Marduk consists of his sacred Spear-head supported by his dragon, that of Nabfi being the Wedge or Stilus, also supported by a horned dragon. But while the other emblems are left sculptured in relief against the field of the stone, that of Nabii is engraved against a temple-tower.[172] It will be noticed that this rises in stages, diminishing in size and set one above the other. The rough engraving may well represent the outward form of Nabû's temple-tower at Borsippa at the time of Merodach-baladan I. In any case, since the emblems on the boundary-stones are associated with temples, the only building it can be intended for is a temple-tower. It thus definitely proves the construction of this class of building in stories or stages, which diminish in area as they ascend. [Illustration: FIG. 30. ROUGH ENGRAVING OF A TEMPLE-TOWER UPON A BOUNDARY-STONE. The boundary-stone is of the period of Marduk-aplu-iddina, or Merodach-baladan I. The engraving represents a temple-tower, before which is a diagon supporting on its back an upright Wedge, the emblem of Nabû. The tower is represented as built in stories, or stopped stages, set one upon the other. (From Brit. Mus., No. 90850.)]