Adapted from Otto Jespersen, Language, Its Nature, Development and Origin
It is not known when or where art music (as distinct from Folk Music) began, but there is evidence the various Mesopotamian Cultures that thrived from 3500 to 500 B.C. already considered music an art, and their writings mention both professional musicians and liturgical music. It is a song, the Sumerian Hymn to Creation, dated before 800 B.C., which is the oldest notated music extant.
Egyptian Musical culture existed by the 4th millennium B.C., and music was prominent in the social and religious life of the Old Kingdom. Egyptian instruments changed significantly as the New Kingdom era (1700-1500 B.C.) began. The change, which may have reflected foreign influence, was from delicate timbre instruments to louder ones and was surely followed by similar changes in singing tone for, over time, a culture's instrumental timbres and vocal tone always tend to match. There are many drawings extant showing that large choruses and orchestras existed in the New Kingdom.
Grecian culture had a highly developed art music that showed signs of both a folk music origin and some Egyptian influence. The poetry of Sappho (600 B.C.) and others was often sung in contests, with melodies and rhythms based on the poetic meters. Singing was associated with all forms of literature and with dance. The ode, the dithyramb (a choral tribute to Bacchus and the forerunner of tragedy), and the drama all employed singers who moved to the rhythm of the music. By 500 B.C. ventriloquism had been described, and both choruses and solo voices were being used in drama. Greek philosophers attached great value to music and to its cultural purposes. The Pythagorean Scales and an initial attempt to publish the complex “Theory of Music” was developed.
The Judaic Culture has preserved some melodies that may go back to 500 B.C. The Psalms of David and the Song of Solomon were sung, and we know of an early presence of professional musicians. Both responsorial (a soloist answered by the congregation) and antiphonal (alternating congregational groups) styles were used in singing the Psalms. After the destruction of the Second Temple, in 70 A.D., Jewish music became exclusively vocal. As the dispersed and transient Jews would learn, the human voice is a readily portable instrument, and communal singing serves to bond its participants in both form and purpose. Like the Egyptians, Jewish singers may have shared musical directions and reminders with hand-signs (Cheirnomie). Cantillation, the intoning of sacred Texts using ancient melodic formulae, written with symbols, was an important musical format. Jewish prayer chants, which were based on ancient melodic lines and often highly ornamented, would have a considerable influence on Christian plainchant.
What we know of Roman Music shows it to have been derived from the Greeks but primarily instrumental and military in nature. Still, Seneca (4 B.C.-64 A.D.) wrote of being disturbed late one night by loud sounds coming from a group of singers practicing vocal exercises.
Singing was such an important part of early Christian Worship that its ritual and music developed together and became almost inseparable. It borrowed music from other religions and from existing secular tunes and slowly developed a form of liturgical chant. It was a style based on sinuous melodies of limited range, expressed in free, un-metered rhythms. These were sung as solos or in unison by unaccompanied male voices. The various scale formats in which they developed were eventually refined into a complex theoretical system of so-called church modes.
As the Christian Church became organized it tried to suppress secularism and secular singing while advancing both itself and its chosen musical style--plainchant. As a result, little evidence remains of the secular musical activity during the early centuries A.D., and we can more easily follow the evolution of singing as it is reflected in the development of sacred music, specifically that of the Latin-speaking Roman Church.
Adapted from (Source)