King Darius ruled the Persian Empire from 521 to 486 BC. Some time around 515 BC, he arranged for the inscription of a long tale of his accession in the face of the usurper Smerdis of Persia (and Darius' subsequent successful wars and supressions of rebellion) to be inscribed into a cliff near the modern town of Bisistun, in the foothills of the Zagros Mountains of Iran, just as one reaches them from the Kermanshah Plain. The inscription was illustrated by a life-sized bas-relief of Darius, two servants, and ten one-metre figures representing conquered peoples; the god Ahura Mazda floats above, giving his blessing to the king. One figure appears to have been added after the others were completed, as was (oddly enough) Darius' beard, which is a separate block of stone attached with iron pins and lead.
The first historical mention of the inscription is by the Greek Ctesias of Cnidus, who noted its existence some time around 400 BC. Also Tacitus mentions it and includes a description of some of the long-lost ancillary monuments at the base of the cliff, where a spring is located. What has been recovered of them is consistent with his description. Diodorus also writes of "Bagistanon" and claims it was inscribed by Queen Semiramis of Babylon.
After the fall of the Persian Empire and its successors, and the fall of cuneiform writing into disuse, the nature of the inscription was forgotten and fanciful origins became the norm. For centuries, instead of being attributed to Darius -- one of the first Persian kings -- it was believed to be from the reign of Chosroes II of Persia -- one of the last. A legend arose that it had been created by Fahrad, a lover of Chosroes' wife Shirin. Exiled for his transgression, Fahrad is given the task of cutting away the mountain to find water; if he succeeds, he will be given permission to marry Shirin. After many years and the removal of half the mountain, he does find water, but is informed by Chosroes that Shirin had died. He goes mad, and throws himself from the cliff. Shirin is not dead, naturally, and hangs herself upon hearing the news.
In 1598 the inscription came to the attention of Western Europe when it was seen by Robert Sherley, an Englishman on a diplomatic mission to Persia in the service of Austria. His party came to the conclusion that it was a picture of the ascension of Christ. Biblical misinterpretations by Europeans were rife for the next two centuries, including such notions as it being Christ and his Apostles, and the tribes of Israel and Shalmaneser of Assyria.
In 1835 Sir Henry Rawlinson, a British army officer training the army of the Shah of Iran, began studying the inscription in earnest. As the town of Bisistun's name was anglicized as "Behistun" at this time, the monument became known as the "Behistun Inscription". Despite its inaccessibility, Rawlinson was able to scale the cliff and copy the Old Persian inscription. The Elamite was across a chasm, and the Akkadian four metres above; both were beyond easy reach and were left for later.
Armed with the Persian text, and with about a third of the syllabary made available to him from the cuneiform expert Georg Friedrich Grotefend, Rawlinson set to work on deciphering the text. Fortunately, the first section of this text contained a list of Persian kings identical to that found in Herodotus, and by matching the names and the characters, Rawlinson was able to crack the form of cuneiform used for Old Persian by 1838.
Next came the remaining two texts. After a stretch of service in Afghanistan, Rawlinson returned in 1843. Using planks he crossed the gap between the Old Persian text and the Elamite, and copied that. He was then able to find an enterprising local boy to climb up a crack in the cliff and rig ropes across the Akkadian writing, so that papier maché casts of it could be taken. Rawlinson set to work and translated the Akkadian writing and language; Edwin Norris and others were the first to do the same for the Elamite. As three of the primary languages of Mesopotamia, and three variations of the cuneiform script, these decipherments were one of the keys to putting Assyriology on a modern footing.
It is believed that Darius placed the inscription where he did specifically to make it tamper-resistant. Even readability -- the text is completely illegible from ground level -- took second place to this imperative. Unfortunately, the Persian king did not account for the pool at the bottom which first caused to a road to be run through the area; the crack into which the local boy wedged himself is the outlet of a small stream of underground water, non-existent at the time of the inscription and now dry, but perhaps the source of the tale of Fahrad's quest for water. It has caused considerable destruction to some figures. Darius also did not anticipate gunpowder, and his monument suffered some damage due to soldiers taking potshots at it during World War II.
The complete text of the Behistun inscription, in transcribed cuneiform and English translation, is available in PDF format from the Case Western Reserve University Digital Library at http://www.cwru.edu/UL/preserve/stack/Sculptures.html.