Before leaving this subject, it is worth noticing that there is a simple explanation for the fact that almost all the Costeriana fragments are on vellum. They have in most cases been found in the bindings of books, and it was the almost invariable habit of Netherlandish binders to line the boards of their bindings with vellum. They used if possible clean vellum, or printed or written only on one side, the used side being pasted down and the clean side exposed. In this way many indulgences have been preserved. In 1473, printing starts simultaneously at Utrecht and Alost, and from that time onward its history is clear. More attention has been paid to the history of printing in the Netherlands than to that of any other country, and the work of Holtrop, Campbell, and Bradshaw offers a firm foundation to rest upon. The first printers at Utrecht were Nicholas Ketelaer and Gerard de Leempt, and their first book was the _Historia Scholastica_ of Petrus Comestor. Though they printed a large number of books, only three are dated, two in 1473 and one in 1474. About 1475 a printer named William Hees printed some books at Utrecht; and in 1478, Veldener moved to that town from Louvain, where he had been printing up to that time. The first printer at Alost was Thierry Martens, an accomplished linguist and scholar, who is supposed by many bibliographers to have learned to print at Venice. He says in the colophon to the _De vita beata libellus_ of Baptista Mantuanus— ‘Hoc opus impressi Martins Theodoricus Alosti, Qui Venetum scita Flandrensibus affero cuncta.’ On this basis the story has arisen, and it is perhaps hardly sufficient to justify the conclusions. The first books, four in number, printed in 1473 and the beginning of 1474, were printed in partnership with John of Westphalia, a printer who in 1474 migrated to Louvain. Thierry Martens continued by himself at Alost for a while, but moved on, in 1493, to Antwerp, and in 1498 to Louvain. According to Van der Meersch, he left Louvain in 1502 to return to Antwerp, but left this town again in 1512, and settled definitely at Louvain till the end of his career in 1529.