ORTHROS. — In the Byzantine rite this word designates the hour of the Divine Office that corresponds to Matins in the Latin Office, including also Lauds. This very long hour, composed somewhat differently according to whether it is a festal, Sunday, or ferial Office, can be divided into four main parts.
1) The six psalms of Matins (= hexapsalmos) 3, 37, 62, 87, 102, 142, recited by the reader while the priest says in a low voice 12 prayers; the Great Collect; some verses from Psalm 117 with troparia;
2) variable psalmody, which includes three cathismata or series of psalms; the last series is Psalm 118 or Psalms 134 and 135 called the polyeleos; followed by a short hymn, formerly the reading of the Fathers, gradual antiphons, and the Gospel (on feast days and Sundays);
3) Psalm 50 with a diaconal prayer, the nine scriptural canticles (almost everywhere omitted), and the Canon, composed of two, three, and most often of 8 odes; after the 6th ode, reading of the Synaxarion;
4) the psalms of Lauds, 148, 149, and 150, the Great Doxology (= the Gloria in excelsis of the Roman liturgy with the second part of the “Te Deum”), the Collect, and the dismissal.
From the fragmentary studies made on the history of the Orthros, one can, with some serious foundation, deduce that the present Orthros, almost fixed since the 10th century, is the fusion of two originally separate hours, joined before the 7th century: the Nocturn or Vigil and the Matins at cockcrow. To the ancient Matins belong Psalm 50, the hexapsalmos (or at least Psalm 62), the scriptural canticles (at least the “Magnificat”), the psalms of Lauds, and the Great Doxology.