As for the falling-off in the yield of the Spanish mines, to which some writers seem to attribute the whole collapse, it could only mean that the Roman Government at length realised what had been as true before and has been as true since, that _all_ gold-mining, save in the case of the richest and easiest mines, separately considered, or of groups of mines which have been acquired at less cost than went to find and open them, is carried on at a loss as against the standing competition of the great mass of precious metal above-ground at any moment, the output of unknown barbarian toil and infinite slave labour, begun long before the age of written history.[220] When it was reluctantly realised that the cost of working either the gold or the silver mines was greater to the State than their product,[221] they would be abandoned; though under a free government private speculators would have been found ready to risk more money in reopening them immediately. As a matter of fact, the Spanish mines were actually worked by the Saracens in the Middle Ages, and have been since. The Romans had made the natural blunder of greed in taking all gold and silver mines into the hands of the State,[222] where speculative private enterprise would have gone on working them at a loss, and so adding--vainly enough--to the total bullion in circulation, on which the State could levy its taxes. Even as it was, when they were losing nothing, but rather checking loss, by abandoning the mines, a falling-off in revenue from one source could have been made good by taxation if the fiscal system had remained unimpaired, and if the former income of Italy had not been affected by other causes than a stoppage of mining output. If the mere cessation of public gold-mining were the cause of a general weakening of the imperial power, and by consequence the cause of the collapse in Italy, it ought equally to have affected the Eastern Empire, which we know to have possessed a normal sufficiency of bullion all through the Dark and Middle Ages, though it had no mines left.[223] The fact is that, when Valentinian and Valens divided the Empire between them, the former chose the western half because he shared the delusion that the Spanish mines were a greater source of real wealth than the fruitful provinces of the east. Those could always procure the bullion they required, because they had produce to exchange for it. Gold mines even of average fertility could have availed no more; and if Italy had remained agriculturally productive she could have sustained herself without any mines.