=4. The Decipherment of the Inscriptions.=--The task of learning to read the inscriptions of Babylonia and Assyria was much more difficult than the decipherment of the Egyptian hieroglyphs, for no such simple key as the Rosetta Stone was at hand. The key that finally unlocked the mystery came not from Babylonia, but from Persepolis in Persia. When Cyrus the Great conquered Babylon in 538 B. C. the Persians had not developed a system of writing. They accordingly adapted to their language the characters of the Babylonian script. The Babylonian script had begun, like the Egyptian hieroglyphs, as a system of picture-writing, in which each picture represented an idea. These had gone through a long development, in which the original picture-forms had been supplanted by conventional characters derived therefrom. In making these characters on clay, one end of a line was always wider than the other, hence the characters are called “wedge-shaped” or “cuneiform.” In the course of the ages the Babylonians had come to use the characters to express both syllables and whole words, and a scribe might mingle these uses of a sign at will in writing a composition. Many of the signs might also express any one of several syllables. In adapting this complicated system, the Persians had the wisdom to simplify it. They selected or constructed a character for each sound, making a real alphabet. Three of the Persian kings, Darius (521-485), Xerxes (456-465), and Artaxerxes II (405-359), wrote their inscriptions in three languages,--Babylonian, Elamite, and Persian,--employing wedge-shaped scripts for all of them. _By Niebuhr._--In the ruins of the great palace of the Persian kings at Persepolis many of these inscriptions in three languages were preserved. These ruins attracted the notice of many travelers from the time that Odoric, a monk, saw them in 1320 A. D., and a number of travelers had made copies of some of them and brought them back to Europe. The inscriptions were a great puzzle. After Alexander the Great (331-323 B. C.) Persia had been subject to foreign powers until 220 A. D., when the Sassanian dynasty (220-641 A. D.) made Persia again an independent kingdom. In the revival of Persian letters that occurred in Sassanian times, a form of the Phœnician alphabet was used, because the old characters of these inscriptions had been forgotten. In 1765 Carsten Niebuhr, a Dane, visited Persepolis and made accurate copies of a large number of these inscriptions. The first correct reading of any of these inscriptions was done from Niebuhr’s copies; (see Fig. 20).