St. Ambrose, Bishop of Milan, a few years later, improved the work of his predecessor, adding words and music of his own. The "Ambrosian Chant" was the antiphonal plain-song arranged and systematized to statelier effect in choral symphony. Ambrose died A.D. 397. Toward the end of the 6th century Christian music showed a decline in consequence of impatient meddling with the slow canonical psalmody, and "reformers" had impaired its solemnity by introducing fanciful embellishments. Gregory the Great (Pope of Rome, 590-604) banished these from the song service, founded a school of sacred melody, composed new chants and established the distinctive character of ecclesiastical hymn worship. The Gregorian chant--on the diatonic eight sounds and seven syllables of equal length--continued, with its majestic choral step, to be the basis of cathedral music for a thousand years. In the meantime (930) Hucbald, the Flanders monk, invented _sight_ music, or written notes--happily called the art of "hearing with the eyes and seeing with the ears"; and Guido Arentino (1024) contrived the present scale, or the "hexachord" on which the present scale was perfected. In this long interval, however, the "established" system of hymn service did not escape the intrusion of inevitable novelties that crept in with the change of popular taste. Unrhythmical singing could not always hold its own; and when polyphonic music came into public favor, secular airs gradually found their way into the choirs. Legatos, with their pleasing turn and glide, caught the ear of the multitude. Tripping allegrettos sounded sweeter to the vulgar sense than the old largos of Pope Gregory the Great. The guardians of the ancient order took alarm. One can imagine the pained amazement of conservative souls today on hearing "Ring the Bells of Heaven" substituted in church for "Mear" or the long-metre Doxology, and can understand the extreme distaste of the ecclesiastical reactionaries for the worldly frivolities of an A.D. 1550 choir. Presumably that modern abomination, the _vibrato_, with its shake of artificial fright, had not been invented then, and sanctuary form was saved one indignity. But the innovations became an abuse so general that the Council of Trent commissioned a select board of cardinals and musicians to arrest the degeneration of church song-worship.