Albert Barnes Commentary Ezra 6:3

"In the first year of Cyrus the king, Cyrus the king made a decree: Concerning the house of God at Jerusalem, let the house be builded, the place where they offer sacrifices, and let the foundations thereof be strongly laid; the height thereof threescore cubits, and the breadth thereof threescore cubits;" — Ezra 6:3 (ASV)

It is difficult to reconcile the dimensions here with expressions in Zechariah (Zechariah 4:10), Haggai (Haggai 2:3), and even Ezra (Ezra 3:12), which imply that the second temple was smaller than the first (compare 1 Kings 6:2). Perhaps the dimensions here are those which Cyrus required the Jews not to exceed.