isaiah 45:3 And I will give thee the treasures of darkness, and hidden riches of secret places, that thou mayest know that I, the LORD, which call thee by thy name, am the God of Israel. - Free Bible Online

      3. treasures of darkness--that is, hidden in subterranean places; a common Oriental practice. Sorcerers pretended to be able to show where such treasures were to be found; in opposition to their pretensions, God says, He will really give hidden treasures to Cyrus (Jer 50:37; 51:13). PLINY (Natural History,, 33:3) says that Cyrus obtained from the conquest of Asia thirty-four thousand pounds weight of gold, besides golden vases, and five hundred thousand talents of silver, and the goblet of Semiramis, weighing fifteen talents.
      that thou mayest know--namely, not merely that He was "the God of Israel," but that He was Jehovah, the true God. Ezr 1:1, 2 shows that the correspondence of the event with the prediction had the desired effect on Cyrus.
      which call . . . thy name--so long before designate thee by name (Isa 43:1).

JFB.