The revival of learning in the 14th century, as might be expected, gave a great stimulus to the production of manuscripts and at the time of the invention of printing from movable types in the middle of the 15th century the manufacture of manuscripts was going on rapidly and there were many great libraries in existence. Matthias Corvinus, King of Hungary in the 15th century, had a library of nearly 50,000 volumes. Duke Frederick of Urbino in Italy had one nearly as large. Duke Frederick had thirty-four copyists regularly employed in his library. It is interesting to note that this library contained perfect copies of practically every book known to be in existence at that time. This fact throws an interesting light on the extent of the world's literature so recently as 500 years ago. Among the earliest of the libraries formed outside of monasteries were those collected by the Arabs of North Africa and Spain. Although some of the early Mohammedan conquerors were ignorant and bigoted fanatics like the destroyer of Alexandria, the Arabs, or Saracens as they are sometimes called, as a whole were a highly civilized people of great culture in art, science, and literature. They were far in advance of their Christian neighbors and continued to be so until their final overthrow in Spain by Ferdinand and Isabella about the time of the discovery of America. The growth of the universities from the 12th century onward played a great part in the multiplication of books and the growth of libraries. Then, as now, the library was the heart of the university. Even more than now the students depended on its contents. Obviously only the richest students could buy any great number of books, and, equally obviously, every student needed to use them, bought what he could, borrowed the rest, and became a book collector for the rest of his life. The university libraries grew by purchase, by copies made on the spot, and by bequests. Then, as now, there were in every university a good number of men "working their way." The copying of manuscripts was their great resource. Naturally all this demand caused the production of many very badly executed manuscripts. This and other abuses were, however, controlled to a great extent by the university authorities who assumed control over the publication and sale of books. Old books, of course, could be freely sold, subject only to careful checking up of the correctness of the copy. New books had to be read three days in succession before the heads of the university or other public judges, always churchmen, and had to receive their sanction before being copied and put on sale.