Darius the king] This was unquestionably Hystaspes, who was raised to the Persian throne after the death of the impostor, Smerdis.
Sixth month] the 6th of the Jewish year, i.e. the month Elul (August-September).
Zerubbabel] A prince of the royal line of Judah, and the accepted civil leader of the people, just as Joshua was the religious leader. He ruled Judah as a Persian province.