The mechanical clock appeared in Europe in late thirteenth century as a new invention. The idea that links it with the development of the urban society and a new need for time telling in cities has been widely extended in historiography, but nowadays its invention and spread is considered a complex phenomenon in which many factors are involved. Science is one of them, but it takes an important role from the sixteenth and seventeenth centuries onwards. This paper attempts to explain the relation of this device with science before the so-called scientific revolution in the early modern period. The mechanical clock in the Middle Ages was used as a prestige object and this was maybe the most important factor for its spread throughout Europe. It was also a practical instrument not only for time telling but also for representing the heavens and the universe. This could be the purpose of its invention. Academics in the thirteenth century were interested in the construction of a self-moving machine to drive a model of the universe. Roger Bacon expressed this desire in a famous letter dated in 1271, which is considered the terminus post quem for the invention of the mechanical clock. The clepsydra had been playing this role since the Antiquity, but the mechanical clock replaced it immediately and the clepsydra virtually disappeared in Europe. Some of the oldest known clocks were astronomical and were designed by academics or by people interested in science like Giovanni Dondi or Richard of Wallingford. Not only academics were interested in the mechanical clock as a model of the Universe, but also people from the highest social strata. Peter IV of Aragon in the fourteenth century owned some clocks, astrolabes and other instruments and he used them as diplomatical gifts. We can find more examples in spanish medieval Royal Courts. The mechanical clock as an instrument for time telling made people time conscious and laid the foundations of a new time concept as an abstract and an individual entity. It was a substantial but a long-term change in Europe, because it became a widely spread accessory and became familiar to a wide social range of people.