Ambrosian chant

In Christian church music, reformed chant introduced by St Ambrose in the 4th century. It retains many features of Middle Eastern religious chant.

The number of available modes (scales) was reduced to four; the interval of the fifth was established as the basis of tonal music, having a lower key note, from which the chant rose and to which it returned; and a higher dominant was established at the fifth, around which the chant was elaborated.