Apart even from the cases of books which had been condemned as heretical, and which had involved in their condemnation the authors, the printers, and the booksellers, the whole system of censorship constituted with its delays, its interference, and its fees or charges, a very heavy burden upon the business of printing and selling books. The details of the methods employed by the censors will be referred to in a later chapter. Their operations, were, of course, not confined to the supervision of books printed in Spain or prepared for the Spanish press. An elaborate system of inspection was instituted for books ordered by booksellers or by individuals from other countries. Large numbers of these foreign publications were destroyed in the customs-houses, while in other cases, as a milder judgment, the supplies were refused admission and had to be returned to the shippers. As a result, the business of importing books could hardly be made profitable, and at times became dangerous. It is not surprising that, in the face of such difficulties and under the hampering influence of such burdens, the book-trade of Spain, during the three centuries following the date of the first Spanish Index, was attenuated and insignificant, and as compared with that of France, Germany, or the Low Countries, played but an inconsiderable part in the community. It is in fact difficult to understand how under these exceptional conditions, any printer-publishers or booksellers should have been able to maintain an existence.