The illuminated book had a unique role in the creation and dissemination of Byzantine art. It was one of the sources to which the artist could and did refer, and the figures and their symbolism appeared in similar creations across the empire in different mediums. Illuminated books also played an important part in the education of young people at this time, helping them to understand the world around them and to learn about Christianity. Byzantium had long been known for its beautiful metalwork and stone carving, but it was the illumination of these texts that made them truly outstanding. The process began with a sketch by the artist that served as a template for those who would follow. This would then be copied by a skilled calligrapher in order to create a perfect version for sale in the marketplace. The choice of subject matter was usually dictated by what was popular at this time, so we find stories from the Bible and saints' lives, but also classical myths and soldiers' tales. Illuminated manuscripts are known by several names including "books of devotion", "liturgical books" or simply "manuscripts". They were created for private use by monks and bishops, but also for sale in the imperial court and large cities such as Constantinople. An average-sized book might have twenty or more illuminations, and some volumes had up to seventy-two pictures.