A number of studies have described the process by which the Byzantine daily service of cathedral type was eventually replaced by one of Palestinian monastic provenance. The Palestinian or Sabaite offices were grafted onto the litanies and prayers of the existing office of the Great Church, thus establishing what became the modern Byzantine office. The office was conceived as uninterrupted praise of God, carried out by three choirs of monks in turn, each doing an eight-hour shift of duty. The ancient office of Hagia Sophia was known as the 'chanted/sung office', the asmatiki akolouthia, a term employed, for example, by the fifteenth-century liturgical commentator, St Symeon of Thessaloniki. Throughout Lent the contemporary office has a series of Vespers readings from Genesis and Proverbs, each preceded by a prokeimenon. As in many other places, Constantinople's 'chanted Vespers' acquired a processional coda. The opening part of the 'chanted Matins' also took place in the narthex.