Alcuin upheld the orthodox doctrine against the views expressed by Felix of Urgel, an heresiarch according to the Catholic Encyclopaedia. Having failed during his stay in Northumbria to influence King Æthelred in the conduct of his reign, Alcuin never returned home. He was back at Charlemagne's court by at least mid-792, writing a series of letters to Æthelred, to Hygbald, Bishop of Lindisfarne, and to Æthelhard, Archbishop of Canterbury in the succeeding months, dealing with the Viking attack on Lindisfarne in July 793. These letters and Alcuin's poem on the subject, , provide the only significant contemporary account of these events. In his description of the Viking attack, he wrote: "Never before has such terror appeared in Britain. Behold the church of St Cuthbert, splattered with the blood of God's priests, robbed of its ornaments." Tours and death In 796, Alcuin was in his 60s. He hoped to be free from court duties and upon the death of Abbot Itherius of Saint Martin at Tours, Charlemagne put Marmoutier Abbey into Alcuin's care, with the understanding that he should be available if the king ever needed his counsel. There, he encouraged the work of the monks on the beautiful Carolingian minuscule script, ancestor of modern Roman typefaces. Alcuin died on 19 May 804, some 10 years before the emperor, and was buried at St. Martin's Church under an epitaph that partly read: The majority of details on Alcuin's life come from his letters and poems. Also, autobiographical sections are in Alcuin's poem on York and in the Vita Alcuini, a hagiography written for him at Ferrières in the 820s, possibly based in part on the memories of Sigwulf, one of Alcuin's pupils. Carolingian Renaissance figure and legacy Mathematician The collection of mathematical and logical word problems entitled Propositiones ad acuendos juvenes ("Problems to Sharpen Youths") is sometimes attributed to Alcuin. In a 799 letter to Charlemagne, the scholar claimed to have sent "certain figures of arithmetic for the joy of cleverness", which some scholars have identified with the Propositiones. The text contains about 53 mathematical word problems (with solutions), in no particular pedagogical order. Among the most famous of these problems are: four that involve river crossings, including the problem of three anxious brothers, each of whom has an unmarried sister whom he cannot leave alone with either of the other men lest she be defiled (Problem 17); the problem of