The Latin "Version II", till now attributed to Adelard of Bath, is edited here for the first time. It was the most influential Euclid text in the Latin West in the 12th and 13th centuries. As the large number of manuscripts and the numerous quotations in other scientific and philosophical texts show, it was far better known than the three Euclid translations made from the Arabic in the 12th century (Adelard of Bath, version I; Hermann of Carinthia; Gerard of Cremona). Version II became the basis of later reworkings, in which the enunciations were taken over, but new proofs supplied; the most...