Columbus made his Spanish voyages in the name of which monarchs' joint title?

Columbus made his Spanish voyages in the name of the Catholic Monarchs: Isabella I of Castile and Ferdinand II of Aragon. Their joint title referred to the royal couple who authorized and supported his expeditions.

The monarchs reached an agreement with Columbus in the Capitulations of Santa Fe, signed on April 17, 1492. The document promised him titles including Admiral of the Ocean Sea, viceroy, and governor of lands he might discover, along with a share of the resulting wealth. Their forces had just conquered Granada, and the crown was seeking new routes and sources of power.

Castile and Aragon were joined through the monarchs’ marriage but remained distinct kingdoms with separate institutions. Isabella provided much of the funding and authorization for the first voyage, so the new territories were formally tied especially to the Crown of Castile. “Habsburg Monarchs” is a later dynastic label and does not identify the rulers who sponsored Columbus.