*Geometry* (1412) of Qadi Zada al-Rumi (1364-1436). Al-Rumi's book was a commentary on the *Fundamental Theorems,* written by al-Samarqandi (1250-1310) and containing a discussion of 35 of Euclid's propositions . The book shown in the image is a later copy of al-Rumi's work, probably written in the sixteenth century. At the top of the page is a discussion of Euclid's Proposition I-5, the "Bridge of Asses" proposition that the base angles of an isosceles triangle are equal. At the bottom, there is a discussion of I-6, the converse of I-5. Al-Rumi was an astronomer and mathematician in the court of Ulugh Beg (1393-1449) in Samarkand. He and his colleagues compiled the first complete star catalogue since the time of Ptolemy.