Although it does not actually claim to have been written in the sixth century BCE, the Book of Daniel gives clear internal dates such as "the third year of the reign of king Jehoiakim," (1:1), that is, 606 BCE); "the second year of the reign of king Nebuchadnezzar, " (2:1), that is, 603 BCE); "the first year of Darius," (9:1), that is 522 BCE); "in the third year of Cyrus," (10:1), that is 547 or perhaps 536). Daniel and his associates are portrayed as Jewish Exiles in Babylon during that period. However, several internal inconsistencies give rise to certain questions and we are forced to ask whether these dates can be taken as the date of composition.
First, who was Belshazzar? The book of Daniel portrays him as the Babylonian king in the first year of whose reign Daniel has his dream of the four great beasts which come up out of the sea. (7:1-14) Belshazzar was said to have been slain after he saw the writing on the wall, at which time Darius the Mede supposedly took over the Babylonian kingdom (5:30) Actually Belshazzar was the son of the Babylonian king, Nabonidus, and he ruled in place of his father when Nabonidus went to live in Teima in the Arabian desert for eight years (c. 552 - 545 BCE.) However, no evidence exists for the assassination of Belshazzar and it is known from conclusive extra-Biblical evidence that in fact Cyrus of Persia took the Babylonian crown from Nabonidus in 539. Darius was the second successor to Cyrus after Cambyses and he (Darius) ascended the Persian throne in 522 BCE. How could the author of the Book of Daniel make such an error if he lived and wrote at the time indicated?
The author of the Book of Daniel seems to place the rule of Cyrus after that of Darius, again an inexplicable error for an author contemporary with these events. Furthermore he makes no mention of the fact that it was the Edict of Cyrus of 538 BCE. which finally allowed the Hebrews to return to Israel. This is a crucial event in the history of the religion of Israel and would surely warrant a mention from any author of that period.
Third it does not seem to be consistent with the facts that the Babylonians are presented as actively persecuting the Jews and attempting to destroy their religion. In fact the Jews lived quite peacefully and had plenty of opportunity to practice their faith in exile in Babylon. The synagogue and the canonization of the Torah have their origins in Babylonian Judaism, as, of course, does the Babylonian Talmud.
Fourth the predictions given by Daniel in the form of the interpretation of dreams and visions are remarkably accurate up to a point. He predicts the rise of four kingdoms (2:31-45). These can readily be identified as the Babylonian, the Persian, the Greek and the divided Greek empire (after the death of Alexander the Great). He continues to tell the "future" with great accuracy. He tells of "a mighty king who shall arise and rule with great dominion" who can be recognized as Alexander (336 - 323 BCE, (11:3). He "predicts" the division of the Greek empire after Alexander's death and the wars between the Ptolemies who rule in Egypt (the "kings of the south") and the Seleucids who rule in Babylon (the "kings of the north"). These general prediction become much more detailed and specific when he predicts the conquest of the king of the south by a king of the north who "shall do as neither his fathers nor his father's fathers have done, scattering among them plunder, spoil, and goods" (11:24). (See also 7:7-10, 8:9-12). This king is "predicted" to cause the sacrifices of the Temple to cease (9:27)and to set up a "desolating sacrilege" in the Temple (12:11) This can be non other than Antiochus IV Epiphanes, the Seleucid ruler of Babylon who profaned the Jerusalem Temple in 167 BCE and set up a statue of Zeus with whom he identified himself. Unfortunately, after these remarkably accurate "predictions" Daniel goes awry at (11:40) when he predicts that this king will be attacked by the king of the south etc. This does not accord with any historical event.
Finally, and of considerable significance, is the fact that the Book of Daniel was never grouped with the Hebrew Nevi'im (the Prophets) but has always belonged to the Ketuvim (the writings). If the author had been accepted to be a sixth century Jew of the Exile his work would have pre-dated Ezra and Nehemiah and would certainly have been considered authoritative enough to group it with the other prophets.
What explanation could make sense of these inconsistencies? The most obvious conclusion would be that the Book of Daniel was written at the time of the profanation of the Temple by Antiochus IV, during the Maccabean revolt which that sacrilege provoked. That would explain why the author is not very precise about sixth century events, why he is so precise about the time of Antiochus, and why he was never counted among the prophets. What other evidence is there to support such a conclusion, apart from the fact that it answers our questions so neatly?
First, stories about Daniel had circulated before the time of Antiochus and had long been used to encourage faithful obedience to and observance of Jewish law. However, all the stories of the book of Daniel relate directly to the persecution under Antiochus: loyalty to the Jewish food laws and the refusal to worship images of other gods had become a question of life and death in Antiochus' crisis-ridden empire.
Second, the name Nebuchadnezzar contains a disguised reference to Antiochus to those acquainted with Hebrew numbering. The Babylonian king of 605 - 562 BCE was in fact called nabu-kuddurri-usur which should be transliterated into Hebrew script as NeuchadRezzar (as it is in eg. Jeremiah 46:2, 39:11). The change of that one letter gives this name the same numerical value in Hebrew (which had no separate numbers and so used letters to represent numbers) as the name Antiochus Epiphanes. This is too coincidental to be accidental and too contrived to be miraculous.
Thirdly, the whole genre of Apocalyptic literature which Daniel represents only developed during the period of crisis and persecution under Antiochus. The few examples of Apocalyptic in the Old Testament are all late, and the popularity of Apocalyptic in the New Testament is indication that it was a relatively new and popular literary form around the time of Jesus.