As we have now reached the period at which artistic music began to develop in all its branches, it will be most convenient to narrate the progress of Roman Catholic church music subsequent to Palestrina's time before passing to other topics. The reader must bear in mind that this music was still designed to be sung without accompaniment, in order that the tone-quality of pure vocal sound might be untainted. When the organ was first used it simply doubled the voice parts, and when independent accompaniments began to be written they considerably altered the character of church music. There were now two distinct schools of Catholic composition,--that of Rome, and that of Venice. The former followed the pure diatonic style of Palestrina; the latter was influenced by the style of Willaert and the chromatic music of Di Rore. The chief masters of the Roman school were Nanini, Vittoria, Anerio, and Allegri. Giovanni Maria Nanini was born in 1540 and died in 1607. He was a coworker with Palestrina, and was the teacher of many of the succeeding composers. His "Hodie nobis coelorum Rex" is still sung at Christmas in the Papal Chapel. Tommaso Ludovico da Vittoria was born about 1540, and died about 1604. He is regarded as one of the greatest of Palestrina's successors. A goodly number of his works has been preserved. His Requiem, written for the funeral of the Empress Maria (1603), is conceded to be his greatest production, and is one of the most notable compositions of that period. "Technically considered, it is a marvellous blending of old independent movement of parts with modern dissonances and progressions. Spiritually considered, it is a wonderful expression of poignant personal sorrow, chastened by religious contemplation and devotion." The marks of change here are the use of the dissonance and the expression of personal feeling. The dissonance in music embraces all those harmonies which sound harsh to persons accustomed only to elementary chords like the tonic, dominant, and subdominant. They are used most freely in modern operatic music, especially that of Wagner, and have always been employed to express passion of some kind. Palestrina avoided them. Felice Anerio (1560-1630) wrote many admirable masses. Gregorio Allegri (1586-1652) is best known as the composer of very fine "Misere" now sung in Holy Week in the Sistine Chapel. This work is regarded as equal to some of Palestrina's.