Fl.160-90 BC. in Bithynia, Anatolia (Turkey). Theodosius's 3 works (the Sphaerics [Kitāb Ukar], On days and nights, and On habitations [Fī al-Masākin]) became known by the title al-mutawassiṭāt (the so-called Middle Books), which were to be studied between Euclid's Elements and Ptolemy's Almagest throughout Islamic lands.