The Daniel 9 prophecy was received in the year after Babylon was conquered by Cyrus (9:1). Daniel knew that LORD revealed to Jeremiah that Babylon will rule for 70 years. These 70 years were from 609 BC to 539 BC. Daniel also knew that God promised to restore Israel to Jerusalem after those 70 years (Dan 9:2). These things caused him to pray for His people and for Jerusalem.
Daniel 9 opens with Daniel noticing that the LORD revealed to Jeremiah that Jerusalem will be desolated for a period of 70 years (Dan 9:2, compare Jer. 25:8-14; 29:10-14). He then prayed earnestly and interceded with God concerning the tragic condition of His backslidden and disobedient people, and for the desolation of Jerusalem and the sanctuary (verses 3-19). In this way the 70 years set the stage for Daniel’s prayer.
When did the 70 years start?
“when seventy years are completed I will punish the king of Babylon and that nation,’ declares the LORD” (Jer. 25:11, 12, compare v1)
The prophecy of Daniel 9 was received “in the first year of Darius the son of Ahasuerus, of Median descent, who was made king over the kingdom of the Chaldeans” (Dan. 9:1). It was, therefore, received soon after the Medo-Persian Empire took over the Chaldean (Babylonian) Empire. The king of Babylon was already punished. This means that the 70 years has already come to an end. But when did it start?
Jerusalem was finally destroyed in BC 586. However, that was not the start of Jeremiah’s 70 years. The 70 years were not the period of Jerusalem’s desolation, but the period of Babylonian rule over Judah and the surrounding nations, as indicated by the following:
“I will send to Nebuchadnezzar king of Babylon … against this land and against its inhabitants and against all these nations round about; and I will utterly destroy them … these nations will serve the king of Babylon seventy years” (Jer. 25:9, 11).
“For thus says the LORD, When seventy years have been completed for Babylon, I will visit you and fulfill My good word to you, to bring you back to this place” (Jer. 29:10).
Judah came under the Babylonian heel in 605 BC (Daniel 1:1), but Babylon’s ruling of nations actually dates from the overthrow of Assyria a few years earlier. After the fall of Nineveh in 612 BC (to the allied forces of the Medes and Babylonians), the Assyrian king Ashuruballit established his government at Harran. This city fell to the Babylonians in 610 BC, and Assyria was finally obliterated when Ashuruballit failed to recapture it in 609 BC. Seventy years later—in 539 BC—Babylon herself was conquered by Cyrus. It is therefore possible to count the seventy years from 609 BC to 539 BC.