The date of man's birth is the symbolic beginning of his marriage with earthly existence, and this was shrouded in a fog of mystery. This mystery was attempted to be known by astrologers, who had knowledge and forecasting tools at their disposal. Such tools included birth horoscopes in their various forms (natal, rectified, anniversary). A skilful astrologer was supposedly able to "read" the fate of the horoscope's addressee from the arrangement of planets, zodiac signs, lunar nodes or fixed stars. And as the belief in the reliability of these predictions was great, so was the demand for horoscopes and the services of astrologers. It is thanks to the fortunately preserved sources that we are able to investigate how great a role knowledge of the date of birth played in the Middle Ages and early modern era in both astrological and astronomical terms.