Charles Ellicott Commentary Ezra 6:15

"And this house was finished on the third day of the month Adar, which was in the sixth year of the reign of Darius the king." — Ezra 6:15 (ASV)

The third day of the month Adar, which was in the sixth year. The event around which this part of the history revolves is dated with due care; it was on the third day of the last month of the ecclesiastical year, B.C. 516-515. Haggai (Haggai 1:15) gives the exact date of the re-commencement: the time therefore was four years, five months, and ten days. But, dating from the first foundation (Ezra 3:10), no less than twenty-one years had elapsed.