While the Bible is a record of human history, it was not written as a history book, and understanding the Old Testament is complicated by the challenge of harmonizing the biblical record with other ancient historical records. Dates and how ancient cultures kept time are essential to understanding the Bible.

In the case of the book of Daniel, there are several important dates to know, because knowing how long Daniel was in Babylon helps one understand his interest in Jeremiah's prophecy (Dan 9:1-2). Nebuchadnezzar conducted three incursions into the Promised Land, which resulted in three deportations of the Jews:

605 B.C. When Nebuchadnezzar conquers the Assyrians and restricts Egypt to its borders, the nation of Judah submits and pays tribute, and the first deportation of Jews occurs, which includes Daniel (Belteshazzar), Hananiah (Shadrach), Mishael (Meshach), and Azariah (Abenego).

Here a potential discrepancy and source of confusion exists: Daniel 1:1 records the invasion of Nebuchadnezzar occurring in the third year of Jehoiakim rule whereas Jeremiah 25:1; 36:1; 45:1; and 46:2 record the invasion as occurring in Jehoiakim's fourth year. Archaeology resolved this issue by discovering that two different ancient systems existed for dating a king's reign. In addition, the divided kingdom of Israel, Judah and Israel, used two different days to herald the new year (i.e. two different New Year's Day were recognized).

1) Accession Year Dating (Post-Dating) - records a king's rule as starting after a new year has commenced, because the year the new king ascended belonged to the previous king. When a king died, accession year dating credits the dead king with the entire calendar year.

Used by the Assyrians and Babylonians, kings David and Solomon adopted the accession year dating, and it was continued by Judah, the Southern Kingdom, when Israel became a divided nation.

Daniel, serving in Babylon and under the accession system, writes of Jehoiakim's rule from the onset of the new year, which is in the context of 607 B.C and used Tishri 1 (September 1) as New Year's Day.

2) Non-Accession Year Dating (Ante-Dating) - records a king's rule as starting in the year of his ascension. With this system, successive kings will share the same year as belonging to their reign.

Long used by the Egyptians, some speculate that the Egyptian system was introduced by Jeroboam when he fled to Egypt to escape the consequences of his rebellion to king Solomon (1 Ki 11:26-40). When the nation of Israel divides into the Northern and Southern Kingdoms, Jeroboam becomes the first king of the Northern Kingdom (1 Ki 12:20).

Jeremiah, using the non-accession year system, records Jehoiakim's first year from the reference point of 608 B.C. and uses Nisan 1 (April 1) as New Year's Day. This is notable, because the Northern Kingdom of Israel ceased to exist in 722 B.C.

597 B.C. When Nebuchadnezzar contests for Egypt which ends in a draw, king Jehoiakim rebels and dies while Nebuchadnezzar returns and forces the surrender of Jerusalem (2 Ki 24:8-14). Jehoiakim's son, Jehoiachin was co-regent; thus, history records Nebuchadnezzar as taking Jerusalem from Jehoiachin. A second deportation took place numbering some 10,000 captives (2 Ki 24:14) which included the royal family, the military, and craftsmen, and leaving behind only the poorest.

586 B.C. King Zedekiah, Jehoiachin's uncle and installed by Nebuchadnezzar, (2 Ki 24:17-18; 2 Chron 36:10-21) initiates a rebellion resulting in the siege of Jerusalem and the complete destruction of the Temple (2 Ki 25:1-21). A third deportation takes place in which all Jews that weren't killed, but remained in the city, were taken except the poorest (2 Ki 25:11-2).

Daniel dates his interest in Jeremiah's prophecy to the "first year of Darius the son of Ahasuerus, of Median descent" (Dan 9:1-2). The identification of "Darius, son of Ahasuerus and of Median descent" has posed a significant problem for scholars. "Darius the Mede" (Dan 11:1) is not mentioned in any extra-biblical historical accounts and is an unknown figure in history. While this fuels skeptical doubt about the Bible's historicity, knowing who "Darius the son of Ahasuerus, of Median descent" is important to establish a date for Daniel's interest in Jeremiah's prophecy.

Of the primary sources of ancient history (i.e. the oldest inscriptions), it is without question that Cyrus the Great conquered and was king of the Babylonian Empire (539 B.C). He was also recognized as the "king of Media," but there is little mention of him with the title of "king of Persia."

Daniel, who probably died during the reign of Cyrus the Great (died in 530 B.C.), mentions two kings while Babylon was part of the Medo – Persian Empire.

Cyrus is mentioned three times in the context of "Cyrus king of Persia" (Dan 1:21; 6:28; 10:1)

Darius the Mede is mentioned by the name "Darius" eight times (Dan 5:31; 6:1, 6, 9, 25, 28; 9:1; 11:1).

Daniel 6 alone mentions the word "king" thirty times in reference to Darius the Mede.

Of all of the candidates that could be "Darius the Mede," Cyrus the Great appears to be the most likely on the basis of several lines of evidence.

All ancient accounts place Cyrus the Great in Babylon after its fall in 539 B.C., and he was about 62 years of age when he took Babylon (Dan 5:31).

It could not be Astyages, because he would have been at least 89 years old in 539 B.C., and many believe that he would have been closer to 100 years of age. Furthermore, his reign ended as king of the Medes when taken captive by Cyrus the Great in 550 B.C.

It could not be Cambyses II, Cyrus the Great's son, who would have been at most 42 years old in 539 B.C.

It could not be Darius the Great, because Darius Hystaspes (549-486 B.C.) was the third Persian king who started his reign in 522 B.C., and he would have been about 20 years old in 539 B.C.

It could not be Ugbaru (of the Babylonian Chronicle), because according to the Nabonidus Chronicle, he died shortly after the fall of Babylon. He was a governor from Gutium who led part of Cyrus the Great's army and successfully took control of Babylon.

It could not be Cyaxares II, the purported son of Astyages (king of the Medes who ruled 585-550 B.C.), because all but one historical record indicate that Astyages did not produce a male heir. The contradictory exception, Xenophon, mentions Cyaxares II but the historian does not recognize him as the king of Babylon.

It is unlikely Gubaru (Greek: Gobryas) of the Nabonidus Chronicle. As one of Cyrus the Great's governors, Gubaru installed other governors in Babylon, and some speculate that he functioned like the "king of Babylon." However, there is little historical information about him, and because of similar names, the details of Ugbaru are sometimes attributed in error to Gubaru.

Ancient cuneiform records attribute Cyrus the Great with all the appropriate positions and titles reserved for the king of the realm of the Chaldeans.

While interpreting Daniel 9:1, many commentators have assumed that the phrase "who was made king over the kingdom of the Chaldeans" referred to Cyrus the Great giving over some responsibility of kingship to another. The logic behind this is that Daniel treats Darius as a real king just as he did with Nebuchadnezzar, Belshazzar and Cyrus, with the exception that Darius "received" the kingdom and was "made" king.

However, there is no historical record of any such arrangement or vassalage which qualified another, besides Cyrus the Great, as king of the realm of the Chaldeans.

More importantly, Daniel writes with a recurring theme, "the most high God is ruler over the realm of mankind and bestows it on whomever He wishes" (Dan 4:32). Never once does Daniel suggest that a human being has the authority to give a kingdom to another. Instead, the kingdom of the Chaldeans was taken away from Belshazzar (Dan 5:22-28) and given to the Medes and Persians (Dan 5:28-31) which was Darius the Mede and historically Cyrus the Great.

Cyrus the Great was a Mede

Cyrus the Great's mother, Mandane, and his grandfather Astyages, were Medes.

Born and raised in Media, Cyrus the Great spoke the language of the Medes and was of the Mede culture.

Through his mother and grandfather, Cyrus the Great inherited Median royal rights and became king over the Medes.

"Darius," like Egypt's "Pharaoh," was a Persian royal appellative title and was not a personal name. Jewish scribes used "Darius" interchangeably with "Artaxerxes" which was another royal appellative title.

Commonly found in many languages of the Ancient Near East, the "wāw" explicativum is a grammatical device that allows the conjunction "and" to be translated as "even, namely" or "that is, for example." Knowing about the "wāw" explicativum clarifies the translation of Daniel 6:28. The NASB translation:

"So this Daniel enjoyed success in the reign of Darius and in the reign of Cyrus the Persian" becomes:

"So this Daniel enjoyed success in the reign of Darius, that is, in the reign of Cyrus the Persian."

The purpose of the "wāw" explicative is to use the second phrase ("the reign of Cyrus the Persian") to explain the first phrase ("the reign of Darius").

For the vast Medo – Persian Empire, the appositional or explicative Hebrew "wāw" construction is used to explain the identity of the same person according to the dissimilar expectations of the audiences of two different locales. Daniel indicates that the royal appellative title Darius is referring to Cyrus the Persian. Another example of the “wāw” explicative can be found in 1 Chronicles 5:26.

"Ahasuerus" was very likely a Median royal appellative title, which referred to an ancestor or progenitor of a prominent royal line and was not a personal name.

The Jews used the title "Ahasuerus" when referring to some of the Persian kings.

Daniel 9:1 - "Ahasuerus" refers to an ancestor of Darius the Mede

Ezra 4:6 - "Ahasuerus" refers to Cambyses II - son of Cyrus II (the Great)

Throughout the book of Esther - "Ahasuerus" refers to Xerxes, who was the fourth Persian king and reigned 486-465 B.C.

Tobit 14:15 (later apocryphal book) - "Ahasuerus" refers to Cyaxares - great grandfather of Cyrus II (the Great)

When examining the family tree of Cyrus the Great and the line of Persian kings of the Achaemenid Empire, one can easily see how "Ahasuerus" is used as a Median royal appellative title. Because the language of ancient times lacked a word for grandson or great grandson, the term "son" would refer to all of the male descendants of a royal line. In this light, Cyrus the Great, king of the Medes, was qualified to be called the "son of Ahasuerus."

By dating to the first year of Cyrus the Great, Daniel's interest in Jeremiah's prophecy (Dan 9:1-2) was around 539 B.C. Because he was deported in 605 B.C., Daniel has been in Babylon for 66 years, and the seventy years of Israel's captivity was near end (Jer 25:11-35). Recognizing that Darius is Cyrus the Great provides clarity in the chronology of events.

Daniel 9: In the first year of "Darius the son of Ahasuerus, of Median descent," Daniel begins to seek God in prayer and supplications with fasting, sackcloth and ashes. Daniel prays, "Oh Lord, the great and awesome God, who keeps His covenant and lovingkindness for those who love Him and keep His commandments." (Dan 9:3-4)

At least eighty years of age, Daniel knows from Jeremiah's prophecy that the Exile was the consequence of unfaithfulness and covenant infidelity; thus, his prayers for forgiveness for his people and himself.

But he knows that the Exile will end, and Daniel calls upon God to act (Dan 9:19). Instead of a message restoring Jerusalem after the seventy years, Daniel receives a message about a restoration in seventy heptads of years!!

It is worthy to note that Daniel 9 was written in Hebrew as this message was for the Jews.

Daniel 6: In the first year of "Darius the Mede," commissioners and satraps (provincial governors) antagonistic to Daniel catch him "praying, giving thanks, and making petition and supplication" to God (Dan 6:10-11). For violating Cyrus the Great's edict, Daniel is cast into the lion's den (Dan 6:12-17).

Because of Daniel's faith in God (Heb 11:32-33), his lack of injury testified to Cyrus the Great of the reality of Daniel's God (Dan 6:23).

Cyrus the Great makes a public proclamation glorifying Daniel's God placing an emphasis on: 1) Daniel's God is alive and active in human history, 2) God's rule is eternal, and 3) God can miraculously rescue and save His people (Dan 6:25-27).

It is worthy to note that Daniel 6 was written in Aramaic as this message was for the Medo – Persian Empire.

Cyrus the Great is so impressed with Daniel and his God that he frees the Jews so that they may return to Jerusalem.

Now in the first year of Cyrus king of Persia, in order to fulfill the word of the Lord by the mouth of Jeremiah, the Lord stirred up the spirit of Cyrus king of Persia, so that he sent a proclamation throughout all his kingdom, and also put it in writing, saying: "Thus says Cyrus king of Persia, 'The Lord, the God of heaven, has given me all the kingdoms of the earth and He has appointed me to build Him a house in Jerusalem, which is in Judah. Whoever there is among you of all His people, may his God be with him! Let him go up to Jerusalem which is in Judah and rebuild the house of the Lord, the God of Israel; He is the God who is in Jerusalem. Every survivor, at whatever place he may live, let the men of that place support him with silver and gold, with goods and cattle, together with a freewill offering for the house of God which is in Jerusalem.'" (Ezra 1:1-4)

Also King Cyrus brought out the articles of the house of the Lord, which Nebuchadnezzar had carried away from Jerusalem and put in the house of his gods; and Cyrus, king of Persia, had them brought out by the hand of Mithredath the treasurer, and he counted them out to Sheshbazzar, the prince of Judah. Now this was their number: 30 gold dishes, 1,000 silver dishes, 29 duplicates; 30 gold bowls, 410 silver bowls of a second kind and 1,000 other articles. All the articles of gold and silver numbered 5,400. Sheshbazzar brought them all up with the exiles who went up from Babylon to Jerusalem. (Ezra 1:7-11)

Then they gave money to the masons and carpenters, and food, drink and oil to the Sidonians and to the Tyrians, to bring cedar wood from Lebanon to the sea at Joppa, according to the permission they had from Cyrus king of Persia. (Ezra 3:7)

But Zerubbabel and Jeshua and the rest of the heads of fathers' households of Israel said to them, "You have nothing in common with us in building a house to our God; but we ourselves will together build to the Lord God of Israel, as King Cyrus, the king of Persia has commanded us." Then the people of the land discouraged the people of Judah, and frightened them from building, and hired counselors against them to frustrate their counsel all the days of Cyrus king of Persia, even until the reign of Darius king of Persia. (Ezra 4:3-5)

However, in the first year of Cyrus king of Babylon, King Cyrus issued a decree to rebuild this house of God. Also the gold and silver utensils of the house of God which Nebuchadnezzar had taken from the temple in Jerusalem, and brought them to the temple of Babylon, these King Cyrus took from the temple of Babylon and they were given to one whose name was Sheshbazzar, whom he had appointed governor. He said to him, "Take these utensils, go and deposit them in the temple in Jerusalem and let the house of God be rebuilt in its place." Then that Sheshbazzar came and laid the foundations of the house of God in Jerusalem; and from then until now it has been under construction and it is not yet completed.' "Now if it pleases the king, let a search be conducted in the king's treasure house, which is there in Babylon, if it be that a decree was issued by King Cyrus to rebuild this house of God at Jerusalem; and let the king send to us his decision concerning this matter." (Ezra 5:13-17)

In the first year of King Cyrus, Cyrus the king issued a decree: "Concerning the house of God at Jerusalem, let the temple, the place where sacrifices are offered, be rebuilt and let its foundations be retained, its height being 60 cubits and its width 60 cubits; with three layers of huge stones and one layer of timbers. And let the cost be paid from the royal treasury. Also let the gold and silver utensils of the house of God, which Nebuchadnezzar took from the temple in Jerusalem and brought to Babylon, be returned and brought to their places in the temple in Jerusalem; and you shall put them in the house of God." (Ezra 6:3-5)

Now in the first year of Cyrus king of Persia—in order to fulfill the word of the Lord by the mouth of Jeremiah—the Lord stirred up the spirit of Cyrus king of Persia, so that he sent a proclamation throughout his kingdom, and also put it in writing, saying, "Thus says Cyrus king of Persia, 'The Lord, the God of heaven, has given me all the kingdoms of the earth, and He has appointed me to build Him a house in Jerusalem, which is in Judah. Whoever there is among you of all His people, may the Lord his God be with him, and let him go up!'" (2 Chron 36:22-23)