The Duomo forms a centre around which clusters much that is interesting, though the time for investigating these various sights will not in reality take long. In the Piazza on the left hand side facing the chief portal stands the Biblioteca Capitolare, a library belonging to the Duomo, and containing some 18,000 volumes in all. The date of some of the treasures contained here is what constitutes the value of this library, and enhances its worth and interest to an untold extent. It is said to be even superior to the Vatican as to the number of the old codexes which it possesses; and which--not including fragments of the fourth century--date from the fifth to the ninth centuries. It was here that Petrarch discovered the letters of Cicero. Niebuhr brought to light the institutions of Gaius, compiled in the reign of Caracalla; and men of letters of all nations and languages find scope here for research and labour. The value of these codexes is incalculable. The greater part are membranous, many of them being palimpsests, others being written in purple having the sacred names inscribed in gold and silver, and all of them offering fields of discovery whereof students (many from England but more still from Germany) are not slow to take advantage. This library contains besides treasures of varied sorts, for here may be seen the baptismal certificate of Prince Charles Edward, the young pretender, dated “Roma, ultima Dicemb. 1720.” A most friendly and learned custodian, Don Antonio Spagnolo, is only too pleased to show the treasures committed to his charge and to explain everything relating to his priceless and loved books to all who are interested in such matters. Opposite this library stands the old disused church of S. Pietro in Cattedra, with a statue of St Peter over the doorway, and some graceful windows of the cusped arched order belonging to the fourteenth century. Close to the Duomo again is the church of St Elena, containing some pictures by Falconetto, Felice Brusasorci, and Niccolŏ da Verona; but the chief interest attaching to this church is the tradition that Dante held here the conference in Latin in which he treated “of the elements of earth and water” (De duobus elementis terrae et acquae); if indeed that much disputed treatise is by him, a point much questioned in these days.