ODEON, a musical theater among the ancient Greeks, built on the same plan as the theater, but smaller, and covered with a roof. The first was fit Sparta. about the middle of the 7th c. B.C. It was called the Skins, and was designed by Theodorus, an archi tect of Samos. Athens had an old one near the Ilissus, but Pericles erected a better one. It stood near the base of the acropolis, on the s.e. side, and its form was said to be imitated from that of Xerxes' tent. It was burned at the siege of Athens by Sulla, and soon after re-erected by Ariobarzaues, king of Cappadocia. There were two other odeons in Athens.one of which, built by Herodes Atticus, had a capacity of 8,000. Each principal Greek city had its odeon; and it was introduced into Rome by Domitian.
O'DER (Lat. Viadrus, Slavon. Vjodr), one of the principal rivers of Germany, rises in the Leseffierg ou the table-land of Moravia, more than 1000 ft. above the level of the sea, and enters Prussian Silesia at Odersberg, after a course of some 60 miles. After traversing Brandenburg in a n.w. direction, it crosses Pomerania, and empties itself into the Stet tiner Haff, from whence it passes into the Baltic by the triple arms of the Dievenow, Peelle, and Swine, which inclose the islands of Wollin and Usedom. The Oder has a course of more than 500 m., and a river-basin of 50,000 sq.miles. The rapid flow of this
river, induced by its very considerable fall, is accelerated by the affluence of several important mountain-streams, and thus contributes, together with the silting at the embouchures of these streams, to render the navigation difficult; great expense and labor being, moreover, necessary to keep the embankments in order, and prevent the overflowing of the river. The Oder has numerous secondary streams, the most impor tant of which are the Oppa, Neisse, Ohlau, Klodnitz, Bartsch, Warte, and the Ihna; and is connected with the Havel and thence with the Elbe by the Finow canal, and with the Spree by the Friedrich- Wilhelms canal. The chief trading port of the Oder is Swinemunde, which constitutes an important center for the transfer of colonial and other foreign goods to northern Germany and Poland. At Ratibor, 17 in. below Oder berg, the river becomes navigable, and is upwards of 100 ft. in breadth; at Oppeln, in Prussian Silesia, it has a breadth of 238 feet. AS a boundary river, it is of considerable importance in a military point of view, and is well defended by the fortresses of Kosel, Grossglogau, Kiistrin, and Stettin.