A book made for use in teaching within an ecclesiastical or university context. School books can be identified from annotations and other markings made for study purposes. Their production increased greatly with the rise of universities around 1200. Stationers emerged as the chief purveyors of such works, which were often (but not necessarily) quite modestly and cheaply produced, sometimes using the pecia system. The subjects of school books varied, from biblical and Patristic works and commentaries, to treatises on grammar, mathematics, astronomy, legal texts (see decretals and digest), medical texts, and classical texts.