Vespers, Compline, Matins, Lauds, Prime, Terce, Sext and Nones. These are periods of prayers which are said through the day in the Divine Office and follow the Hours which are found in Breviaries or a Book of Hours, which is really just a type of Breviary for laymen. The tradition of the hours finds its roots in the Jewish tradition which prayed at the third, sixth and ninth hours of the day. Terce (9a.m.), Sext(noon), and Nones(3 p.m.) are Latin for three, six and nine, or the third, sixth and ninth hours of the day. The addition of the others comes from the Rule of St. Benedict, and are said at sundown (Vespers), evening (Compline), midnight (Matins), sunrise (Lauds) and the first hour (Prime).
In religious communities it was the responsibility of the monks to keep track of the hours so that prayers were said at the correct time. Using stars and constellations at night, and position of the sun in the day helped to keep the time. Devices like sundials in the day or an astrolabe at night were useful in keeping time in good weather, but bad weather rendered these useless. Candles which marked the hours or water clocks (clepsydra) would also have been helpful in determining the hours. However such devices were not always available in monasteries and so the use of liturgical prayers and psalms was employed to keep time. This responsibility was given to one of the monks who was called the Significator Horarum.
The Significator Horarum would Sing psalms or recite the Pater Noster (Lord’s Prayer) to keep time when weather prevented the use of star charts or sundials. This would have been like counting “one Mississippi, two Mississippi” in children’s games. When enough prayers were said to equal the right amount of time, the Significator Horarum would then notify another monk to wake or gather the community for prayers.
The Latin translation for Significator Horarum means a caller of the hours or indicator or time. In a way he is like a human clock, or rather a grandfather clock signaling the passage of time. In time new inventions would come along like mechanical clocks which took care of the problem of keeping time and maintaining the liturgy of the hours. When you stop to think about it, the divine office is really a continual prayer which has been going on for almost 1500 years, a great portion of which was maintained by the vigilant Significator Horarum.