K. A. Heinrich Kellner, Heortology (1908)
“ The want of uniformity in the duration of Advent in different parts of the Church is due to the fact that local Churches, conformably to the ancient discipline, acted independently of each other. Thus, in Rome Advent lasted only four weeks, as we gather from the Gregorian sacramentary, which provides three Sundays in December with collects de adventu Domini, and a dominica vacans; [160] in the Appendix, however, five Sundays are reckoned before Christmas. ”
