Daniels Prophesy Of 70 Weeks

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The key to understanding the 'seventy-sevens' of Daniel 9 is the phrase 'from the going forth' (Dan 9:25). This determines the beginning of the period.

Now in the first and second verse we are told when this happened and what Daniel's concern was.

“In the first year of Darius the son of Ahasuerus, of the seed of the Medes, which was made king over the realm of the Chaldeans;
2 In the first year of his reign I Daniel understood by books the number of the years, whereof the word of the LORD came to Jeremiah the prophet, that he would accomplish seventy years in the desolations of Jerusalem.” (Dan 9:1-2)

Darius the Mede was Cyrus the Persians counterpart.
They had the same 'first year'.
The 'going forth' of the command was to/from Cyrus.

“Now in the first year of Cyrus king of Persia, that the word of the LORD by the mouth of Jeremiah might be fulfilled, the LORD stirred up the spirit of Cyrus king of Persia, that he made a proclamation throughout all his kingdom, and put it also in writing, saying,
2 Thus saith Cyrus king of Persia, The LORD God of heaven hath given me all the kingdoms of the earth; and he hath charged me to build him an house at Jerusalem, which is in Judah.(Ezr 1:1-2 KJV)

“That saith of Cyrus, He is my shepherd, and shall perform all my pleasure: even saying to Jerusalem, Thou shalt be built; and to the temple, Thy foundation shall be laid. (Isa 44:28 KJV)

According to historical sources Cyrus first year was 538 BC.

So if the 'going forth' was 538 BC and the period was 'seventy-sevens' or 490 years then the end of that period would be 48 BC. (We already know that Daniel was concerned about Jeremiah's 'seventy years' so 'seventy-sevens' is 7 x 70 years).

Question: What historical event happened in 48 BC?