From Imperial Spain: 1469-1716, by J. H. Elliott (Penguin, 2002), 2nd ed., Kindle Loc. 2149-2165:
Two separate economic systems continued to exist side by side: the Atlantic system of Castile, and the Mediterranean system of the Crown of Aragon. As a result of the expansion of the wool trade and the discovery of America, the first of these was flourishing. The Crown of Aragon’s Mediterranean system, on the other hand, had been gravely impaired by the collapse of Catalonia, although there was some compensation for Catalonia’s losses in the increased economic activity of late fifteenth-century Valencia. Ferdinand’s pacification and reorganization of Catalonia, however, enabled the Principality at the end of the century to recover a little of its lost ground. Catalan fleets began to sail again to Egypt; Catalan merchants appeared once more in North Africa; and, most important of all, a preferential position was obtained for Catalan cloths in the markets of Sicily, Sardinia, and Naples. But it is significant that this recovery represented a return to old markets, rather than the opening up of new ones. The Catalans were excluded from direct commerce with America by the Sevillian monopoly, and they failed, for reasons that are not entirely clear, to break into the Castilian market on a large scale. They may have shown a lack of enterprise, but they also seem to have suffered from discrimination, for as late as 1565 they were arguing that the Union of the Crowns of 1479 made it unreasonable that Catalan merchants should still be treated as aliens in Castilian towns. As a result of this kind of treatment, it is scarcely surprising that Catalonia and the Crown of Aragon as a whole should have continued to look eastwards to the Mediterranean, instead of turning their attention towards the Castilian hinterland and the broad spaces of the Atlantic.
Castile and the Crown of Aragon, nominally united, thus continued to remain apart – in their political systems, their economic systems, and even in their coinage. The inhabitants of the Crown of Aragon reckoned, and continued to reckon, in pounds, shillings, and pence (libras, sueldos, and dineros). The Castilians reckoned in a money of account – the maravedí [named after the Moorish Almoravid dynasty]. At the time of the accession of Ferdinand and Isabella the monetary system in Castile was particularly chaotic.