The Diocese borders Burgos and Logroño on the north, Soria and Saragossa on the east, Soria and Guadalajara on the south, and Segovia on the west; and includes the civil provinces of Soria and Burgos, with a small portion of Segovia. It is the ancient Uxama and has 1250 inhabitants. Burgo de Osma, the episcopal see, has 3000. The origin of the diocese is obscure: some refer it to St. James the Apostle, others to the reign of Constantine the Great. Flórez alleges it only as "probable" that it existed in the first centuries when bishops, to escape persecution, used to establish their sees in obscure places; hence it might have been selected rather than Clunia, the capital of a judicial district. John, Bishop of Osma, signed the acts of the Synod of Toledo, in 597; Gregory signed at the synod of 610; Gila signed the acts of the fourth and fifth Councils of Toledo, and sent as his delegate to the eighth, Godescalchus, who afterwards succeeded him, and signed the eleventh; Severian signed at the twelfth, and Sonna at the thirteenth and sixteenth. After the Arab invasion the bishops of Osma continued, as titulars, in Asturias: a letter against Adoptionism, addressed to Elipandus, Archbishop of Toledo, is signed by Eterius, Bishop of Osma, and Beatus, a priest. The "Chronicon Albedense" mentions Felmirus, Bishop of Osma, in the time of Alfonso III (821).

The succession was then lost until Fernán Gonzalez, Count of Castile, conquered Osma, placing in its see Silo, a monk of Arlanza. The place was again lost, and the see with it; but eventually Alfonso VI called in the Cluniacs, under Bernardo Salvitá (later Archbishop of Toledo), and made Pierre de Vitunis, a French monk, Bishop of Osma. Then began protracted boundary disputes with the Bishops of Oca and of Burgos, compromised at the Council of Husillos, in Palencia, in 1088; others followed with the Bishops of Sigüenza and of Tarazona, to whose jurisdiction Alfonso the Fighter assigned the territory taken from Castile, finally settled in the time of Alfonso VII, at a council at Burgos, where Cardinal Guido was present as papal legate. After Vituris, the see was occupied by Pedro, formerly archdeacon of Toledo, canonized as St. Peter of Osma. Finding the old church in ruins he chose as the site for a new one El Espinar. His successor, the Frenchman, Raymond Salvitá, continued the boundary controversy and the building of the church, and, having been transferred to the See of Toledo, was succeeded by Beltrán (1128). To provide for the building of his church, Bishop Beltrán obtained a commutation of the Vow of Santiago for a visit and alms to Osma; he also founded the Confraternity of the True Cross, the brethren of which bound themselves to leave legacies for the building of the cathedral.

Bishop Diego de Acebes accompanied St. Dominic against the Albigenses. In 1232 Bishop Juan Dominguez, finding the cathedral again too small, rebuilt it, with the exception of some cloister chapels, still to be seen, spared out of respect for the memory of St. Peter of Osma. It is in the transition style from Romanesque to ogival, with later improvements and additions. Pedro Gonzalez, Cardinal de Mendoza, Bishop of Osma in 1478, built the marble pulpit. Bishop Pedro Acosta, who had previously occupied the See of Oporto, brought with him the Italian Giovanni di Juni, who (1540) embellished the re-table of the high altar with figures of St. Peter of Osma and St. Dominic, and also designed the university. Bishop Acosta founded (1557), in Aranda de Duero, the "Sancti Spiritus" convent of the Dominicans, and the chapel of the Santo Cristo del Milagro, originally designed as a chapel of St. Dominic de Guzmán. The organ on the right is the gift of Bishop Martin Carrillo in 1641, that on the left, of the chapter in 1765. The chapel of the Cristo del Milagro contains an altar and re-table, with an inscription giving the traditional legend, built by Bishop Andrés de Soto. With the assistance of Bishop Garcïa de Loaisa, Melendez de Gumiel, Dean of Osma, built the chapel of St. Peter, now the chief patron of the diocese. The chapel of Our Lady of the Thorn-bush, planned by Bishop Pedro Arastegui, corresponds to the Santo Christo. In 1506, Bishop Alonso Enriquez, rebuilt the cloisters. Between 1736 and 1744 Pedro Agustín de la Cuadra built the new tower adjoining the west wall in the Barocque style. Joaquín de Electa, confessor to Charles III, built a chapel for Juan de Palafox, Bishop of Osma, completed in 1781. The frescoes are by Mariano Maella.

The bishops of Osma were formerly lords of the city. At the petition of Bishop John II, Alfonso VIII issued a warrant confirming the lordship to the cathedral chapter, and left instructions that the lordship of Osma, with its castle, should be given to Bishop Mendo (1210-25) in recompense for his services at the battle of Las Navas de Tolosa (1212). King John I granted the castle of Osma to Bishop Pedro González de Frias, Bishop Pedro de Montoya surrounded Burgo with a wall, in 1456. Bishop Pedro Alvarez de Acosta founded the university at his own expense, and in 1578, adjacent to the cathedral, the consistorial buildings, prison, and public granary. Bishop Sebastian Perez (1582-83) transferred the seminary from the college of the university to the Casas del Cortijo (Farm Buildings), and Fernando de Acebedo (1610-15) began the Seminary of S. Domingo de Guzmán, which Bishop Joaquín Eleta reconstructed in 1783 after plans made by the engineer Sebastini. Sebastian de Arévalo rebuilt the Hospital of S. Agustin, founded in 1468 by Pedro de Montoya.

Soria, the capital, disputes with Osma the right to the episcopal see. There is the church of S. Pedro, restored by Alfonso I of Aragon, in 1108, and made collegiate in 1152 by John II, Bishop of Osma. Over the altar of the retro-choir is an "Entombment of Christ", by Titian. It was rebuilt by Bishop Acosta. Near Soria are the Romanesque ruins of the monastery of S. Juan de Duero and the hermitage of St. Saturius, patron of the city. The convent of La Merced at Soria once had for its superior the dramatist Gabriel Tellez (Tirso de Molina), to whom are due the building and painting of the sacristy of Nuestra Señora de la Merced.

CORVALÁN, Descripción histórica del Obispado de Osma (Madrid, 1788); DE QUIRÓS, Vida de S. Pedro de Osma; FLÓREZ, España sagrada, VII (Madrid, 1789); RABAL, España, sus monumentos . . . Soria (Barcelona, 1889); DE LA FUENTE, Historia de las Universidades de España, II (Madrid, 1885); Biografia eclesiástica (Madrid, 1848-68).

RAMÓN RUIZ AMADO