In the fourth century, St. Ambrose, Bishop of Milan, introduced antiphonal singing, where the choir sings alternate verses of a psalm or hymn. In the fifth century, St. Gregory the Great, Pope of Rome, standardized the liturgy and established a system of eight musical modes. This system, known as Gregorian chant, became the primary form of music in the Catholic Church for centuries.
During the Middle Ages, various other forms of church music, such as liturgical dramas, polyphony, and organ music, began to develop. Polyphony, where two or more musical lines are sung simultaneously, became important in the 12th century.
In the 16th century, Martin Luther initiated the Protestant Reformation. This led to the development of different styles of church music, such as Lutheran chorales and Anglican chant. These genres remain important parts of Christian worship today.
The 19th and 20th centuries saw a renewed interest in the study and performance of early church music, such as Gregorian chant and the works of Palestrina. There has also been an outpouring of new sacred music composed in a variety of styles.