OSMA, DIOCESE of. - A diocese in the province of Soria in Old Castile (Spain). It has an area of 8,549 sq. km., with a population of 188,900 inhabitants, all Catholics, distributed among 429 parishes, served by 315 diocesan priests and 80 religious; it has a seminary, 8 male and 20 female religious communities (Ann. Pont., 1952, p. 304). The seat of the diocese is in the small town of Burgo de O.
The beginnings of the diocese are somewhat uncertain. One of its incumbents, Giovanni, attended the Council of Toledo in 597. Devastated during the occupation of the Moors (8th-11th cent.), the diocese was re-established in 1088, and in 1103 s. Pietro di O. took possession of II. In the middle of the 16th cent., Bishop Pietro Alvarez de Acosta enlarged, under the direction of the Italian artist Giovanni di Juni, the College of S. Caterina, later made a University and suppressed by Carlo III in the 18th cent.
The diocese, formerly suffragan of Toledo and since 1851 of Burgos, comprises part of the provinces of Burgos and Soria and a small strip of that of Segovia. The Cathedral, dating from the 13th cent., has the high altar by Giovanni di Juni (1554). The patron of the diocese is s. Pietro di O.