could find strength to return home. Hovhannes Imastaser also contributed to the standardization of the Armenian prayer book and Psalter. Hovhannes Imastaser's work in mathematics is represented by the volume Haghaks Ankiunavor Tvots (Concerning Polygonal Numbers). This work indicates a profound knowledge of all important ancient and medieval mathematicians, including Pythagoras, Euclid and Aristotle. Hovhannes Imastaser translated into Armenian the works of the following classical scholars: Philo of Alexandria, Dionysius the Areopagite, Gregory of Nyssa, Porphyry, and, as mentioned, Aristotle and Euclid. In 1084, Hovhannes Imastaser became involved in the project of developing so-called Minor Armenian Calendar, which included all 365 days plus one additional day. Eventually, his work on calendars led to the invention of a perpetual or eternal calendar. One of the most important citations of Hovhannes Imastaser reflects his understanding of the role of the empirical method in science. 150 years before Roger Bacon, Hovhannes Imastaser famously noted: “Without experimentation, no opinion can be considered probable and acceptable; only experiment produces confirmation and certainty.” References Bibliography External links Armenian musicologists Armenian philosophers Armenian mathematicians 12th-century Armenian writers 12th-century mathematicians 11th-century Armenian writers