Jamieson, Fausset and Brown on Isaiah 45:3

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 (Jr 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 (Is 43:1).