Before the discovery of the _silver_ mines of Tasco, on the western slope of the Mexican Cordillera, in the year 1522, America supplied only _gold_ to the Old World, and consequently, Isabella of Castile was obliged, already in 1497, to modify greatly, the relative value of the two precious metals used for currency. This was doubtless the origin of the Medina edict--which changes the old legal ratio of 1:10.7. Yet Humboldt has shown that, from 1492 to 1500, the quantity of gold drawn from the parts of the New World then known, did not amount, annually, to more than about one thousand pounds avoirdupois;--and the Pope Alexander VI., who, by his famous Bull, bestowed one half the earth upon the Spanish kings, only received in return, from Ferdinand the Catholic, some small fragments of gold from Hayti, to gild a portion of the dome of the Basilica of Santa Maria Maggiore;--a gift that was suitably acknowledged in a Latin inscription in which the offering is set forth as the first that had been received by the Catholic sovereigns from India. Although the income of treasure must have increased somewhat, yet the working of the American mines did not yield three millions of dollars yearly until 1545. The ransom of Atahualpa amounted, according to Gomara, to about four hundred and twenty-five thousand dollars of our standard, or fifty-two thousand marks of silver, whilst, the pillage of the Temples at Cuzco, if Herrera is to be credited, did not produce more than twenty-five thousand seven hundred marks, or a little more than a quarter of a million of our currency.[14]