One of the most significant literary achievements of the Anglo-Saxons was the establishment of vernacular prose as an acceptable medium both for the dissemination of knowledge on a wide range of subjects and for the provision of moral instruction and entertainment. By the time of the Norman Conquest, English was being used for scientific and medical works, legal documents, historical records and religious instruction of all kinds, thus fulfilling a public and official role in society. Translations and reworkings of Latin texts had made available to educated laymen and clergy alike key works on philosophy and theology, world history and geography, along with travellers' tales and accounts of the east - occasionally even fiction - while for students in the monastic schools there were textbooks on computus (the science of calculating moveable Christian feasts, such as Easter) and on grammar and rhetoric. Even the gospels and a considerable portion of the Old Testament had been rendered into English.