This thesis tries to answer the question of how the night office sluthō d-lilyō has developed in the Syrian Orthodox Antiochian tradition as it is expressed in the Syrian Orthodox prayerbook of ܫܚܝܡܐ Šḥimō - which is the prayerbook used on ordinary weekdays and Saturdays throughout the liturgical year except for the great Lent. One of the main liturgical scholars of the 20th century, Robert F. Taft S.J. (+ 2018), refined the methods of Anton Baumstark (+ 1948) and Juan Mateos S.J. (+ 2003), and studied how the Liturgy and Liturgy of the Hours have grown during the centuries. This thesis uses the method(s) of Taft and studies how the night office has grown by comparing the structure of this office in six manuscripts from the Monastery of Mor Gabriel in Tur-’Abdin – one of the major monasteries in the Syrian Orthodox world. The oldest manuscript in our study is dated to 1474 C.E. (perhaps the oldest dated MS of the Šḥimō in the entire world). Few studies have looked into how the Šḥimō tradition has changed during the centuries and in this thesis we will take the night office as an example of liturgical growth and development.