Then Darius the king made a decree, and search was made in the house of the rolls, where the treasures were laid up in Babylon. In the house of the rolls - בית ספריא beith siphraiya, the house of the books, the king's library. This is the first time we hear of a library.
Related Commentaries of Ezra 6:1
Ezra 6:1
1 Then Darius the king made a decree, and search was made in the house of the rolls,a where the treasures were laid up in Babylon.