Had it not been for one piece of indirect evidence, it would have seemed nearly certain that they were not employed by the Mesopotamian races.  In some of the royal palaces, however, small humps of fine clay have been found, bearing the impressions of seals, and exhibiting traces of the string by which they were attached to documents, while the documents themselves, being of a different material, have perished.  It seems probable that in these instances some substance like paper or parchment was used; and thus we are led to the conclusion that, while clay was the most common, and stone an ordinary writing material among the Assyrians, some third substance, probably Egyptian paper, was also known, and was used occasionally, though somewhat rarely, for public documents.

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The number of characters is very great.  Sir H. Rawlinson, in the year 1851, published a list of 216, or, including variants, 366 characters, as occurring in the inscriptions known to him.  M. Oppei t, in 1858, gave 318 forms as those “most in use.”  Of course it is at once evident that this alphabet cannot represent elementary sounds.  The Assyrian characters do, in fact, correspond, not to letters, according to our notion of letters, but to syllables.  These syllables are either mere vowel sounds, such as we represent by our vowels and diphthongs, or such sounds accompanied by one or two consonants.

The vowels are not very numerous.  The Assyrians recognize three only as fundamental—­a, i, and u.  Besides these they have the diphthongs ai, nearly equivalent to e, and au, nearly equivalent to o.  The vowels i and u have also the powers, respectively, of y and v.

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From these sounds, combined with the simple vowels, comes the Assyrian syllabarium, to which, and not to the consonants themselves, the characters were assigned.  In the first place, each consonant being capable of two combinations with each simple vowel, could give birth naturally to six simple syllables, each of which would be in the Assyrian system represented by a character.  Six characters, for instance, entirely different from one another, represented pa, pi, pu, ap, ip, up; six others, ka, ki, ke, ak, ik, uk; six others again, ta, ti, tu, at, it, ut.

If this rule were carried out in every case, the sixteen consonant sounds would, it is evident, produce ninety-six characters.  The actual number, however, formed in this way, is only seventy-five.  Since these are seven of the consonants which only combine with the vowels in one way.  Thus we have ba, bi, bu, but not ab, ib, ub; ga, qi, gu, but not ay, iq,ug; and so on.  The sounds regarded as capable of only one combination are the mediae, b, q, d; the aspirates kh, tj; and the sibilants ts and z.