Breton literature may refer to literature in the Breton language (Brezhoneg) or the broader literary tradition of Brittany in the three other main languages of the area, namely, Latin, Gallo and French – all of which have had strong mutual linguistic and cultural influences. Breton literature can be categorised into an Old Breton period, from the 5th to 11th century; and a Middle Breton period, up to the 17th century. The period break is marked by the Norman invasions of the 10th and 11th centuries which triggered an exodus out of Brittany. Many Old Breton extant words are glosses in Latin manuscripts from the 9th and 10th centuries, now scattered in libraries and collections throughout Europe. It is likely there was a highly developed oral tradition during the Old Breton period. And on the evidence of Breton names, it would appear that Old and Middle Breton literature inspired much of Arthurian literature, the story of Tristan and Iseult and the Lais of Marie de France. The oldest surviving manuscript in the Breton language (dating to the end of the 8th century) is kept at Leyden University, Netherlands, and predates the oldest text referenced in French by more than a century. It is generally assumed by specialists that this is the most ancient text in a continental Brythonic language and was studied by the late Professor Léon Fleuriot (1923–1987). The manuscript itself is a fragment of medicinal recipes composed of plants suggesting that Breton may well have been used by people of learning at the turn of the 11th century. Although written in Latin the Breton Gospel (British Library, Egerton 609) is an important literary work in terms of the wider scope of Breton culture. Amongst other things it attests to a high degree of learning and, presumably, monasterial wealth in Brittany comparable to that of Lindisfarne and Kells. The Gospel Book manuscript dating from the 9th century contains the Latin text of the four Gospels, along with prefatory material and canon tables – an interesting admixture of traditions.