Another obstacle to the diffusion of learning was the incompetence of the copyists. It is true that at the great universities _stationarii_, who supplied the text-books in use to students, were certified and subjected to the control of special censors called _peciarii_. Yet their number was not large, and when they quitted the routine to which they were accustomed their incapacity betrayed itself by numerous errors.[93] Petrarch's invective against the professional copyists shows the depth to which the art had sunk. 'Who,' he exclaims, 'will discover a cure for the ignorance and vile sloth of these copyists, who spoil everything and turn it to nonsense? If Cicero, Livy, and other illustrious ancients were to return to life, do you think they would understand their own works? There is no check upon these copyists, selected without examination or test of their capacity. Workmen, husbandmen, weavers, artisans, are not indulged in the same liberty.'[94] Coluccio Salutato repeats the same complaint, averring that the copies of Dante and Petrarch no more correspond to the originals than bad statues to the men they pretend to represent. At the same time the copyists formed a necessary and flourishing class of craftsmen. They were well paid. Ambrogio Traversari told his friend Giustiniani in 1430 that he could recommend him a good scribe at the pay of thirty golden florins a year and his keep. Under these circumstances it was usual for even the most eminent scholars, like Petrarch, Boccaccio, and Poggio, to make their own copies of MSS. Niccolo de' Niccoli transcribed nearly the whole of the codices that formed the nucleus of the Library of the Mark. Sometimes they sold them or made advantageous changes. Poggio, for example, sold two volumes of S. Jerome's 'Letters' to Lionello d'Este for 100 golden florins. Beccadelli bought a Livy from him for 120 golden florins, having parted with a farm to defray the expense. It is clear that the first step toward the revival of learning implied three things: first, the collection of MSS. wherever they could be saved from the indolence of the monks; secondly, the formation of libraries for their preservation; and, thirdly, the invention of an art whereby they might be multiplied cheaply, conveniently, and accurately. [Footnote 93: In Milan, in the fourteenth century, when the population was estimated at about 200,000, the town could boast of only fifty copyists. Tirab. loc. cit. cap. 4.]