There is little doubt, that the invention of the mechanical clock as one of the first inventions made in Western Europe without clear antitypes in antiquity or the Muslim world had serious consequences for thinking and behaviour even in the everyday life at the end of the 13th century. This shift exerts influence on modern Western societies that continues to today. It is therefore significant to consider, why this invention was made in Western Europe, what were the preconditions of this invention and (if it is possible), to fix the date of this invention as clear as possible.

The first question shall be answered by examining the changes in the concept and cognition of time and its relation to historical circumstances, the expectation of the Judgement Day in near future and the broader extension of the idea of purgatory. For the second question new concepts in natural sciences as the analysis of the laws of crank and pneumatic devices on the one hand, the discussion on the role and interpretation of Aristotelian philosophy in Paris between 1270 and 1277 on the other can help to clear the terms of the invention. The question for the date shall be discussed by the help of the common handbook of astronomy at medieval universities and a special addendum to it for the terminus post quem, special developments in music theory for the terminus ante quem. Finally a short outlook of the consequences of this invention will be given.

Management of time – even more important than measurement of time – is one of the most fundamental tasks and challenges of every human society. From the era in which first communities settled on one place for more than one generation as in Anatolia around 10.000 years B.C. [...] observation of the sky, especially sun and moon enabled people to fix important dates for agriculture in the course of year. So it is not astonishing that thousands of years ago monumental constructions, perhaps used for religious rituals too, had been erected to celebrate solstice in summer and winter and/or monitor the different overlapping periods of the moon. These long-period observations had been conducted carefully, so it became not only an obvious fact for priests or rulers of these societies that the different cycles and repetitive events on heaven and earth do not match in a simple way. It was also clear, that complex structures for the management of time could not become reduced to one single and tangible unit for time-measurement. The result of this comprehension of time-units we can see in our calendric system today. We live with additional days to correct the difference between the duration of the solar year and a discrete number of days, whilst our months differ from the duration of moon-phases (some societies even preferring a double calendar related to the moon and sun).

The interesting point for our considerations here is, that even for the construction of time-units which are based on astronomical given facts, there remain underlying determinations which are not derived from these astronomical facts but instead from religious or even abstract principles. So for instance a year, consisting of 13 months with 28 days per month – which would fit better to moon-phases and even to the Jewish order of the week – would have only a difference of a little bit more than one day to the correct solar year.

This would offer a simpler and more practical solution than our current system of months and years which is based on the religious and number conceptions in the area of Mesopotamia around 3000 years ago [...]. The tension between the physical and astronomical facts and the every-day-use of time units influenced not only our practical knowledge of time, it seems that it also affects theories and understanding of time fundamentally, especially in the matters of time-structure which cannot become related to these physical and astronomical facts in an other than arbitrary way. Concepts of time and time-measurement get some special high-handed character. This can be seen in the concept and measurement of the hour, which links the astronomical based time-units as day, month and year with the corporal rhythms of breathing, heart beating and pulse. The duration of an hour is apparently highly arbitrary, though attempts to introduce other durations (e. g. to establish a decimal system also in time-measurement [...]) had not been successful. The reasons for this may be found in deep-rooted traditions of dividing the duration of a day; perhaps psychological or psychosomatic factors may also play a role. The crucial point, however, is, that the duration of an hour is not a fixed quantity of time until the invention of mechanical clocks.

This seems amazing, especially because the hour is the most important time-unit for every-day- life – everybody uses it day to day – and since antiquity different tools for a sufficient measurement of the duration of an hour had been invented. This could be such a rather simple (but expensive) tool like a candle, a sand-clock or much more sophisticated constructions like the so-called clepshydra (water-clock [...]). The reason for the on-going success of the “breathing” hour, an hour whose duration depends on seasonal fluctuations of the length of day-light and is measured by the help of sundials, apparent from its fit best to the organization of life in societies which depend a lot, not to say at all, from daylight. It makes no sense for a peasant to stay at home after sunrise in summer only because a clock tells him that it is not yet 6 o’clock in the morning. It's the same for a stonecutter on a building site of a cathedral; he should not get up in darkness in winter only because a clock demands this. His work – lighted by candles or even torches – cannot be done as accurate as necessary without daylight. Even in libraries work could not start before dawn and had to end at dusk – (although here questions of fire hazard may play a role too). The only relevant social class in medieval societies, which could have benefitted from an hour-measurement, based on a clear and fixed duration would have been monks. They had to organize their so-called “Hours” of singing and preaching in day and night-time: in summer they had little time to sleep, because the obligations of the Hours do not left over much time in night. In winter there was little time to work during the day for the same reason.

However, the mechanicalclock was not invented in a monastery in the late 13th century, as is commonly supposed [...]. Be that as it may, the fact, that this mechanism was not only successful but also widely adopted in Western Europe immediately after its invention, needs a convincing explanation.

But another point also needs such an explanation. The mechanical clock driven by a weight and possibly by the help of a balance wheel is certainly a smart invention; compared with mechanic constructions and automata like the famous mechanism of Antikythera [...], the astronomical clocks build in Muslim territories like al-Jazaris automata (especially his so called “Elephant Clock”) and the connected considerations of al-Ghazali [...] or described in the Libros del saber de astronomia from Spain [...] it is rather simple. To make matters even worse: Muslim astronomical research and science had such a high level, that’s not possible to suppose that the lack of a clear and fixed time-unit for the hour should for them felt less uncomfortable for the further processing of the observation data than Robertus Anglicus expressed in 1271 [see below].

For me the only possible explanation for both questions is: the concept and the perception of time had changed in Western Europe in the 13th century so much and in such a way, that a stable, calculable and countable unit was not only useful, it became necessary. This shift is clearly connected to Western Europe, so it must have reasons, which appear in Western Europe only or in a special way.

I see two different but syndetic reasons for this shift. Both lie in the religious sector and are related to special, but in the consequence fundamental transformations of the interpretation of Christian doctrine. The first one is strongly related to a phenomenon, which appears consistently in the history of church and more or less Christian societies. Christ has promised his Parousia, so his believers want to be prepared for his second coming. Special external influences like cruelties, wars or epidemic events, special years (as the year 1000 P.C.) could let grow more or less nebulous apocalyptic feelings and phenomena or give rise to chiliastic and apocalyptic movements. As in other eras (such as the 16th century) this role could be played by calculations, which are done by the help of the very dark and unclear relations to the prophecy of the end of all days with numbers, which could be found in the Bible.

Such calculations are done in small circles, but their ideas could penetrate larger groups in the society especially if the special historical situation let emerge some resonance for the expectation that the end of time is near. It is clear, then, why people want to have a clear and countable unit of time to calculate this end. But why was this end expected in the second half of the 13th century? On the one hand the end of the gospel of Matthew [...] there Jesus assigned his disciples to bring his message to all people until the end of the world, was seen as prophecy of the end. In the moment all nations, the whole mankind had heard the Christian message, Jesus should not have any reason to hesitate to come again. This situation at the end of the 13th century seems not any more an expectation far away. On the other hand, the influence, even the existence of churches outside the roman- catholic tradition disappeared after the 4th crusade nearly totally.

Concurrent religious movements could be seen as heretics, who are not able to hinder the coming of Christ but may be part of apocalyptic struggles and wars. In this situation, a (later banned) Jewish rabbi from Spain, Abraham Aboulafia [...] started hidden activities based on his cabalist readings of the Scripture, the so called Sepher Jezira and other texts, to prepare for the end of the present aeon he expected in the nineties of the century. It’s highly astonishing, that he was strongly supported by Christian monks and followers of Joachim of Fiore, who had speculated one hundred years ago about a new order of the world, he called regnum tertium. They even helped Aboulafia to realize his – at the end, failed – plan to convince the Pope to become a Jew [...]. In a situation in which Christians and Jews work together to prepare the end of all times, the time itself shifts from a given structure of every-day-life which takes place in the natural order and rhythms of days, weeks, months, seasons and years, and to a “time that is left”, to years, months, days even hours which not only have to be calculated to be prepared but to be used as a “last chance” before no chance is left.

This leads directly to the second point: as much as the time “here on earth” becomes “time that is left”, a last chance, the time in the expected world after death also gains a clear time-structure. Hence in the early church sometimes a “third place” between heaven and hell was reflected, the idea of purgatory became more and more popular and influential in Western Europe after the nonappearance of Christ in the year 1000. Hence this doctrine became dogma in the roman-catholic church not before 1439 [...] the general acceptance and influence of the idea, that every person – in normal cases – will be punished for a fixed time in purgatory before this person can ascend to paradise. This can be seen in Dante`s Divina Comedia, where the descriptions of the “third place” take a whole part of the book.

But if the punishment in purgatory and its duration is clearly connected with special misbehaviour or special sins, then it should be clear, how the calculation of this duration of punishment works. Though this duration normally is seen as a number of years and not of months, days or even hours – in comparison to eternity even years are a “short time” – when time becomes a real currency in front of heaven’s gate, then it should be clear how this currency is counted and how the calculation works. The duration of the fixed unit of time here is not as much a question how long or short it is. Importantly, only a fixed unit can be counted and can be related to other currencies: prayers, pilgrimages, acts of mercy and – as to be expected – at the end: money. It’s not a surprise that, if time in the after-world can be paid, then time also on earth can be paid, can be bought or sold. For this a tool like the mechanical clock is absolute necessary.