Sovereign ownership of mines and taxation were fundamental principles governing the mining economy of the territories of the Castilian crown during the medieval period. Ownership of mines meant that mineral wealth, discovered or undiscovered, belonged to the crown estate. Only the sovereign could grant mining rights to ‘private’ persons and impose mineral taxation. Particularly during the last three centuries of the Reconquista (thirteenth to fifteenth centuries), these principles were used to unify the situation in those territories falling under the sway of a sovereign with expansionist ambitions. Increasing globalisation of the metal trade in the thirteenth century and the formation of capital markets in Europe firmly put the Castilian crown in competition with other economic agents aiming to win a monopoly in metallic wealth. Castile's mining laws aspired to solve the ensuing tension by attracting merchant capital to the mines, aiming to absorb the comparative advantages of mining capital. In a protracted process, the mineral laws of the sixteenth century were a testimony to the decisive influence of the sovereign in the history of mining.