A mysterious inscription that (as the story goes) appeared on the wall during a banquet celebration in Babylon, the same night that its king, Belshazzar, was assassinated. According to historical records, this would have been the night of October 5/6, 539 B.C.
"Belshazzar the king made a great feast for a thousand of his lords, and in front of the thousands he was drinking... They drank wine, and praised the gods of gold, and of silver, and of brass, of iron, of wood, and of stone." (Daniel 5: 1, 4)
First of all, it should be said that this was a rather bad time to be throwing a party. Even as the celebration was going on, the combined forces of Media and Persia were overrunning Babylon's borders and sweeping toward the city. Belshazzar's father, Nabonidus (who was still in some capacity the nation's true king) was leading the skirmishes on the frontier, and was hiding out in Borsippa while his son filled in for him as King. And what does Belshazzar do? He goes to his buddies and says, "Hey, my dad's got these casks of wine down in the cellar..." Typical, eh?
"At that moment the fingers of a man's hand came forth and wrote upon the plaster of the wall of the king's palace across from the lampstand... And this is the writing that was written, ME'NE, ME'NE, TE'KEL, U-PHAR'SIN" (Daniel 5: 25)
Obviously, Belshazzar was puzzled and frightened by this. He called forth his wise men and declared "Whoever shall read this writing, and show me the meaning of it... shall be the third ruler in the kingdom" (That is, the next in power after his father and himself). Interestingly enough, even with an offer like that on the table, the wise men couldn't read the writing or figure out what it meant.
To understand that, you need to remember that this was ancient Aramaic we're talking about. There's no vowels to speak of, and so any group of letters could have more than one meaning, depending on context. Think "MN, MN, TKL, PRSN". And the only obvious context between those three letter-groups is that they could all be read as units of money.
"MN" could be "mina", "TKL" could be the Aramaic word for "shekel", and "PRSN" could be the word "divisions", which stood for half-minas or half-shekels. The wise men were likely confused as to why a hand would materialize out of thin air just to write them a descending list of coins. Of course, if these wise men had already been at the party for a while and were boozing it up with the King, that may have also had something to do with it...
Eventually, Belshazzar's wife remembers a Hebrew named Daniel, who had interpreted a prophecy for her father King Nebuchadnezzar many years earlier, and decides to call him in. Daniel, with the help of a little divine inspiration, is able to solve the puzzle right off the bat.
"ME'NE, God has numbered your kingdom and finished it." (Daniel 5: 26)
See, the mina was one of the principal units of money in the ancient world, and from it came the Aramaic word "mene", which meant "numbered out". Possibly, the word was repeated twice to indicate that it refered to both Belshazzar and his father Nabonidus. As the saying goes, their days were numbered.
"TE'KEL, you are weighed in the balances and are found wanting." (Daniel 5: 27)
"Tekel", on the other hand was written only once and in the singular. Likely, this one was meant for Belshazzar only. What the wise men failed to catch on this one is that shekel was both a unit of coinage and of weight. And one shekel wasn't a whole heck of a lot. Belshazzar was being judged deficient, and-- considering the circumstances-- for obvious reason.
"PE'RES, your kingdom is divided and given to the Medes and the Persians." (Daniel 5: 28)
The last one was trickiest of all. "Upharsin" (or as some Bibles transliterate it: "parsin") was a pluralized verb that literally meant "divided" or "divisions". However, Daniel slyly turns it to its singular form, "peres", once again directing it straight at the King. At the same time, he makes it even more obvious what other word could be formed from those same letters: their word for "Persian".
In effect, God was making a pun. A deadly serious pun, but still a pun.
That same night, the advancing army diverted the Euphrates River and invaded the city. Babylon had been conquered by Cyrus the Persian. And now you know... the rest of the story.