Daniel 9:1, 2

In the first year of Darius the son of Ahasuerus, of the lineage of the Medes, who was made king over the realm of the Chaldeans

in the first year of his reign I, Daniel, understood by the books the number of the years specified by the word of the LORD through Jeremiah the prophet, that He would accomplish seventy years in the desolations of Jerusalem.