Ohrid: One of the most important cities of southwestern Macedonia and an administrative, religious, commercial and cultural center of the region. Nine churches, erected between the 9th and the 14th centuries, survive to this day and may be counted among the most important artistic and cultural monuments of the Byzantine world.
Organon: Title of a collection of philosophical treatises, found in the Corpus Aristotelicum (that is the corpus of the works of Aristotle) and comprising treatises on methodology.
Orhan:Ruler (emir) of the Ottomans (1326-62), son and successor of Osman I, the founder of the Ottoman dynasty. During his reign the Turks drove the Byzantines out of almost the entire region of Asia Minor and began their expansion into the Balkans.
Orsini, John:Count of Kephalenia and despotes of Epiros (1323-1335/6). For a short period of time he managed to annex the southern part of Thessaly to the state of Epiros. In 1355/6 he was murdered by his wife, "queen" Anna, who wanted to secure the rule of the despotate for herself and her son, Nikephoros II.
Ottomans:Turkish dynasty initially ruling over an emirate, from around 1300, and later, after 1453, over the Empire which replaced the Byzantine Empire. The cradle of the Ottomans, who took their name from the founder of their dynasty, Osman, was the area west of the Sangarios river, in which they settled after the dissolution of the Seljuk state, and from which they began their holy war against the Byzantines.