Not as incomplete, indeed, as their history, for religious rites are not subject to many changes, and the progress of religious ideas does not keep pace with the constant changes in the political kaleidoscope of a country; but, it is evident that no exhaustive treatment of the religion can be given until the material shall have become adequate to the subject.
III.
Before proceeding to the division of the subject in hand, some explanation is called for of the method by which the literary material found beneath the soil has been made intelligible.
The characters on the clay tablets and cylinders, on the limestone slabs, on statues, on altars, on stone monuments, are generally known as cuneiform, because of their wedge-shaped appearance, though it may be noted at once that in their oldest form the characters are linear rather than wedge-shaped, presenting the more or less clearly defined outlines of objects from which they appear to be derived.

At the time when these cuneiform inscriptions began to be found in Mesopotamia, the language which these characters expressed was still totally unknown.

Long previous to the beginning of Botta's labors, inscriptions also showing the cuneiform characters had been found at Persepolis on various monuments of the ruins and tombs still existing at that place.

The first notice of these inscriptions was brought to Europe by a famous Italian traveler, Pietro della Valle, in the beginning of the seventeenth century.

For a long time it was doubted whether the characters represented anything more than mere ornamentation, and it was not until the close of the 18th century, after more accurate copies of the Persepolitan characters had been furnished through Carsten Niebuhr, that scholars began to apply themselves to their decipherment.