In the first year of Darius - See the notes at Daniel 5:31, and Introuction to Daniel 6 Section II. The king here referred to under this name was Cyaxares II, who lived between Astyages and Cyrus, and in whom was the title of king. He was the immediate successor of Belshazzar, and was the predecessor of Cyrus, and was the first of the foreign princes that reigned over Babylon. On the reasons why he is called in Daniel Darius, and not Cyaxares, see the Introduction to Daniel 6, Section II. Of course, as he preceded Cyrus, who gave the order to rebuild the temple Ezra 1:1, this occurred before the close of the seventy years of the captivity.
The son of Ahasuerus - Or the son of Astyages. See Introduction to Daniel 6 Section II. It was no unusual thing for the kings of the East to have several names, and one writer might refer to them under one name, and another under another.
Of the seed of the Medes - Of the race of the Medes. See as above.
Which was made king over the realm of the Chaldeans - By conquest. He succeeded Belshazzar, and was the immediate predecessor of Cyrus. Cyaxares II ascended the throne of Media, according to the common chronology, 561 b.c. Babylon was taken by Cyrus, acting under the authority of Cyaxares, 538 b.c., and, of course, the reign of Cyaxares, or Darius, over Babylon commenced at that point, and that would be reckoned as the “first year” of his reign. He died 536 b.c., and Cyrus succeeded him; and as the order to rebuild the temple was in the first year of Cyrus, the time referred to in this chapter, when Daniel represents himself as meditating on the close of the captivity, and offering this prayer, cannot long have preceded that order. He had ascertained that the period of the captivity was near its close, and he naturally inquired in what way the restoration of the Jews to their own land was to be effected, and by what means the temple was to be rebuilt.