P. L. Jacob, Military and religious life in the Middle Ages and at the period of the Renaissance (1870)
“ St. Cyprian, who lived in the third century, says that prayers were said at Tierce in honour of the descent of the Holy Ghost, at Sexte in memory of the Crucifixion, and at None to commemorate the death of Christ. Half a century earlier Tertullian wrote that, independently of the mystic traditions consecrated by prayer, the Church, in establishing the canonical hours, wished to conform to the secular division of the day.Vespers (Vespera) , so called from the star Vesper, which rises as the sun is setting, also dates from the origin of the liturgy. ”
