12th century in a calligraphy and an architecture which, though still somewhat awkward, showed unmistakable signs of power and experience, and at the end of that century and in the first half of the 13th both arts reached their climax and made their boldest flights. The topography of later medieval writing is still being studied; national varieties can, of course, be identified but the problem of distinguishing features becomes complicated as a result of the development of international relations, and the migration of clerks from one end of Europe to the other. During the later centuries of the Middle Ages the Gothic minuscule continued to improve within the restricted circle of de luxe editions and ceremonial documents. In common use, it degenerated into a cursive which became more and more intricate, full of superfluous strokes and complicated by abbreviations. In the first quarter of the 15th century an innovation took place which exercised a decisive influence on the evolution of writing in Europe. The Italian humanists were struck by the eminent legibility of the manuscripts, written in the improved Carolingian minuscule of the 10th and 11th centuries, in which they discovered the works of ancient authors, and carefully imitated the old writing. In Petrarch's compact book hand, the wider leading and reduced compression and round curves are early manifestations of the reaction against the crabbed Gothic secretarial minuscule we know today as "blackletter". Petrarch was one of the few medieval authors to have written at any length on the handwriting of his time; in his essay on the subject, La scrittura he criticized the current scholastic hand, with its laboured strokes (artificiosis litterarum tractibus) and exuberant (luxurians) letter-forms amusing the eye from a distance, but fatiguing on closer exposure, as if written for other purpose than to be read. For Petrarch the gothic hand violated three principles: writing, he said, should be simple (castigata), clear (clara) and orthographically correct. Boccaccio was a great admirer of Petrarch; from Boccaccio's immediate circle this post-Petrarchan "semi-gothic" revised hand spread to literati in Florence, Lombardy and the Veneto. A more thorough reform of handwriting than the Petrarchan compromise was in the offing. The generator of the new style (illustration) was Poggio Bracciolini, a tireless pursuer of ancient manuscripts, who developed the new humanist script in the first decade of the 15th century. The Florentine bookseller Vespasiano da Bisticci recalled later in the century that