Mediana is a term peculiar to Roman liturgy and is applied to the fifth Sunday in Lent, to the Wednesday and Saturday which precede this Sunday, and to the week embracing these three days. The term first occurs in a letter of Pope Gelasius, written in 494, in which he says that ordinations of priests and deacons should only be performed at certain seasons on Saturday evening, namely the fasts of the fourth, seventh and tenth months, which are the original Embertides, on the first Saturday in Lent, which is in the fourth and later Embertide, and on the Saturday medianae quadragesimae. The term occurs again in the next century when Pope Pelagius I (556–561) appointed this mediana septimana paschae as a season for ordinations. The text of Gelasius is quoted in the Liber Diurnus, of which the earliest manuscript dates from the seventh to the eighth century; in a letter of Gregory II of 715; and in the eleventh Canon of the Roman Council of 743.

The preface to the Book of Common Prayer, entitled Concerning the Service of the Church since 1662, but before that simply The Preface, was derived substantially from the preface to the revised Breviary of Quiñones, which was one of the sources for the revised daily offices of the Church of England. It appeals from what it considers the corruptions of the medieval office to the ‘godly and decent order of the ancient Fathers’. This order, it says, was devised for the systematic reading of holy scripture in the offices of the Church, and it was the intention of the compilers of the English Prayer Book to restore such a regular order of reading for the instruction of the people. It represented a revolt against three features of the lessons in the medieval breviary: first, against the frequent interruptions of the reading of scripture in course by the occurrence of feasts with proper lessons; secondly, the lack of completeness and continuity in the lessons themselves; and thirdly, the use of non-biblical material in the lessons. Even if the daily office of the breviary, which is based on the ecclesiastical year, were not interrupted by any immoveable feasts having proper lessons, it would still not provide for the reading of the whole of scripture, as its lessons are too short, and also the variable lessons are confined to the night office.