This example of cunieform writing is known as the "Nabonidus Chronicle." The original artifact is maintained at the British Museum. Image online, courtesy Livius.org. PD
Scholars tried to figure out what the words on ancient clay tablets meant, but they had no guidelines.
Georg Grotefund, a high school teacher in Germany, was sure the cuneiform wedges represented some type of alphabet. Using two different inscriptions from a gate at Persepolis (in modern Iran), Grotefund isolated what he believed were royal names.
He was right, but he couldn't really do more without a kind of Rosetta Stone for cuneiform. The Rosetta Stone (with its three inscriptions in hieroglyphs, demotic Egyptian and Greek which all say the same thing) was rediscovered in Rashid (Rosetta), Egypt in 1799 by Napoleon's army.
Because a young French Egyptologist, Jean Francois Champollion, could work with two of the three languages, he was able to unlock the secret (the links are part of his famous letter to Monsieur Dacier) to the third language: Egyptian hieroglyphics. (Follow these links to hear the possible pronunciation of ancient Egyptian.)
Scholars trying to decipher cuneiform writing needed a similar break. They got it from an ancient king of Persia mentioned in the Bible: Darius I.
A great ruler in the 5th Century B.C., Darius conquered many people, not just the Hebrews. He commemorated his genealogy and many conquests in three languages written in cuneiform script on the face of a cliff in Bisitun, Persia (the Zagros Mountains of today's Western Iran).
To make sure no one could ever deface his monument, Darius had the ledge sheared off. For centuries after his death (this link depicts his tomb), no one knew what the drawings signified.
In 1835, an Englishman, Sir Henry Creswicke Rawlinson, was serving as consul at Baghdad. An Orientalist who had some understanding of Sanskrit and Avestan (languages closely related to Old Persian), Rawlinson decided to scale the rock at Bisitun. Working under dangerous conditions, he copied the inscription (called the Behistun Inscription) on the mountain. Nearly ten years passed before he had it all.
Once he had the entire inscription - written in Old Persian, Susian (the Iranian language of Elam), and Assyrian - Rawlinson deciphered the Old Persian engraving since it was closest to a language he already knew. But cracking the other languages did not go as smoothly.
Susian (Elamite) was not related to either Sanskrit or Avestan. And, although Assyrian was related to other Semitic languages (like Hebrew and Aramaic), it was complicated by all the old Sumerian signs and symbols.
When scholars trying to decipher the Susian/Elamite and Assyrian inscriptions finally cracked the mystery of those ancient languages, each man sealed his translation. If they were similar, people would believe the hidden world of cuneiform writing was finally open to further study because the scholars had not collaborated.
The translations were close enough. Each language written on the Behistun Inscription said the same thing: How great Darius was and how great was his ancestry. (Scroll down to the text for the Darius columns to read the translation in English.)