Catabasia

Catabasia (Καταβασία). was an anthem or short hymn in the Greek offices. so called because the two sides of the choir come down (καταβαίνουσι) into the body of the church and unite in singing it. It often occurs between the "odes" of a "canon;" and its construction is that of any other "troparion." Sometimes two "catabasive" occur together between each ode, as on the Sunday after Christmas-day, where each pair consists of the first troparion of the corresponding odes of the two canons for Christmas- day.