the wolf, goat, and cabbage (Problem 18); and the problem of "the two adults and two children where the children weigh half as much as the adults" (Problem 19). Alcuin's sequence is the solution to one of the problems of that book. Literary influence Alcuin made the abbey school into a model of excellence and many students flocked to it. He had many manuscripts copied using outstandingly beautiful calligraphy, the Carolingian minuscule based on round and legible uncial letters. He wrote many letters to his English friends, to Arno, bishop of Salzburg and above all to Charlemagne. These letters (of which 311 are extant) are filled mainly with pious meditations, but they form an important source of information as to the literary and social conditions of the time and are the most reliable authority for the history of humanism during the Carolingian age. Alcuin trained the numerous monks of the abbey in piety, and in the midst of these pursuits, he died. Alcuin is the most prominent figure of the Carolingian Renaissance, in which three main periods have been distinguished: in the first of these, up to the arrival of Alcuin at the court, the Italians occupy a central place; in the second, Alcuin and the English are dominant; in the third (from 804), the influence of Theodulf the Visigoth is preponderant. Alcuin also developed manuals used in his educational work – a grammar and works on rhetoric and dialectics. These are written in the form of a dialogue, and in two of them the interlocutors are Charlemagne and Alcuin. He wrote several theological treatises: a De fide Trinitatis, and commentaries on the Bible. Alcuin is credited with inventing the first known question mark, though it did not resemble the modern symbol. Alcuin transmitted to the Franks the knowledge of Latin culture, which had existed in Anglo-Saxon England. A number of his works still exist. Besides some graceful epistles in the style of Venantius Fortunatus, he wrote some long poems, and notably he is the author of a history (in verse) of the church at York, Versus de patribus, regibus et sanctis Eboracensis ecclesiae. At the same time, he is noted for making one of the only explicit comments on Old English poetry surviving from the early Middle Ages, in a letter to one Speratus, the bishop of an unnamed English see (possibly Unwona of Leicester): ("Let God's words be