Until about 1550 practically all art-music in western Europe was choral. Though the first important steps in the development of music were taken in Italy, devotion to the principles of unison Gregorian chant kept the polyphonic idea from gaining a foothold there until the fourteenth century. As we have seen, vocal counterpoint was the offspring of northern musicians, and under their care and guidance it developed into its most complex and perfected form. The first centre of activity was Paris, during the twelfth and thirteenth centuries. From this point the art was gradually disseminated to the northward and its development was continued through the experimentation and theorizing of the musicians of northern France and Flanders (the Gallo-Belgic School, 1360-1460). After these zealous apprentices had made ready the crude tools of composition, there appeared real masters who strove earnestly to convert the elaborate technical forms and devices of vocal counterpoint into vehicles for the expression of musical feeling and religious devotion. These masters were the Netherlanders (from 1400 to 1550), whose mission it was to perfect the forms and material of musical composition, and, working from the standpoint of musical science, to compel these forms to serve the expressional purposes of the art. So well did they accomplish these two ends that for nearly two centuries all of western Europe gave musical allegiance to the Netherlanders and looked to them for teachers, composers, and choir leaders. During this period the Low Countries were the musical headquarters of Europe.