Time had been measured from antiquity, using sundials on clear days and waterclocks, sand glasses, and segmented candles at other times. The mideveal church followed a variation of the time used in the roman empire, where the day was divided into twelve hours (which changed in length with the season) and four watches of the night.

St. Paul had ordained prayer without ceasing. If unceasing prayer was taken literally, no work would get done. The Church compromised by increasing the number of prayer events to eight. Those became the canonical hours with their old Roman names: Matins, Lauds, Prime, Terce, Sext, Nones, Vespers, and Compline.

Notice that only four of those times carry numerical names. That's because the Romans numbered only the daylight hours. Prime, the first hour, was the beginning of the measured day at 6:00 AM. Terce, the third hour, was 9:00 AM.

 The clock is said to have been invented to solve the problem of waking the monk who's job was to ring the bells to call the community to nocturnal prayers.  Thus, the first clock was an alarm clock.

Multiple accounts of early clockmaking show a picture of this clock as an example of an early Italian monastic alarm.  I am very suspicious of this for a number of reasons, but it does have many features of early clocks.  It has a twenty-four hour dial that rotates, and the time is shown by a fixed pointer.  The alarm is tripped by a pin fixed in the rim of the dial.  The time is measured by the oscilations of the castle shaped balance wheel, suspended by a thread from the top of the clock.  A falling weight on a cord wrapped around the larger barrel, drives the balance back and forth, by means of an escapement.

A clock like this wouldn't have been accurate to more than fifteen minutes gained or lost per day, but it was better than nothing.  In a sunny climate, where it could be frequently checked by sun-dial, it would have been fairly useful.

There is no doubt that clocks were used in monastic communties:  here is a picture of St. Augustine by Botticelli, dated 1480:

That thing over the figure's shoulder is an iron monastic alarm.  It is used in the painting ostensibly as a symbol of mortality (note the armilary sphere denoting scientific learning), but really to show off the sitter's familiarity with luxury objects.

This type of iron chamber clock was made until the mid eighteenth century.  Here's a look at a slightly later one with a fixed twelve hour dial and a balance arm with adjustable weights so the timekeeping could be adjusted:

Soon it was realized that the mechanism could be made on a larger scale, and ring the tower bells by itsself.  In another episode we'll look at some early tower clocks.