The 'house of the archives' (Ezr 6:1 RV; AV 'rolls') was a part of the 'treasure house' (Ezr 5:17) of the Persian kings at Babylon, in which important State documents were preserved.
"Now if the king is so inclined, let a search be conducted in the royal archives there in Babylon in order to determine whether King Cyrus did in fact issue orders for this temple of God to be rebuilt in Jerusalem. Then let the king send us a decision concerning this matter."
So Darius the king issued orders, and they searched in the archives of the treasury which were deposited there in Babylon.
NET Bible copyright © 1996-2006 by Biblical Studies Press, L.L.C. NetBible