The area had previously been part of the
Diocese of Lilybaeum (Marsala), a port 27 mi (22.0 km) to the northwest, which was captured by the Muslims in 827. At that time it was a suffragan diocese of the Patriarchate of Constantinople, having earlier been dependent on Rome. Under the Normans, Lilybaeum was not reestablished. In the struggle of the Saracens against the Normans for the possession of
Sicily,
Mazara was hotly contested, especially in 1075 when
Roger I of Sicily emerged victorious. In 1077, the port city of Trapani was captured. Mazara was captured in 1092, and, with the permission of
Pope Urban II, a new diocese of
Mazara del Vallo was established at the
seaport of Mazara (Mazzara) in 1093.
Norman Sicily In 1093, Count Roger granted the territories forming the diocese of Mazara to Bishop Stephen of Rouen, his
consanguineus (blood relative), and his successors. The territory of Trapani was included in the territory Mazara del Vallo. Roger was insistent that the dioceses he established should belong to the Roman rite, and that the bishops should be consecrated by the pope. He applied the same policy with the foundation of the diocese of Squillace in Calabria in 1096. The privileges of Mazara were confirmed by
Pope Paschal II in the bull "Omnipotentis Dei nutu" of 15 October 1100. In 1130, at the request of King
Roger II of Sicily, the
antipope Anacletus II granted the archbishops of Palermo the right to consecrate three bishops of Sicily: Syracuse, Agrigento and Mazara. This made the three dioceses suffragans of the metropolitan of Palermo. This arrangement was confirmed by
Pope Adrian IV in 1156. In 1176, a part of the diocesan territory was transferred to the abbey of Monreale. The diocese was obligated to pay an annual pension to the Chapter of
Santa Maria Maggiore in Rome. It is noted that in 1101, Basilian monks were in possession of the monastery of Santa Maria de Alto and at Santi Niccolo e Giovanni. Benedictine monks had a monastery at San Michele Archangelo. There was also a Basilian monastery of San Michele, founded 1127 by George of Antioch, the admiral of King Roger II. The monastery of Sainte-Marie de l'Abita was founded in 1383, by Enrico Vintimille, the lord if Abita.
Cathedral The cathedral, founded by Count Roger and Bishop Stefano, was later embellished by Bishop Tustino (1157–1180). Dedicated to the Holy Savior, it had a Chapter composed of four dignities and eighteen Canons. The dignities are: the Cantor, the Archdeacon, the Dean, and the Treasurer. the right of appointment of the Cantor belongs to the Pope. If a vacancy in one of the other dignities or a canonicate occurs between January and June, the right of appointment belongs to the Pope, and if the vacancy occurs between July and December, to the Bishop . Bishop Carlos Impellizzeri (1650 – 1654) and Bishop Giovanni Lonzano had the bell tower and most of the façade constructed. A fair was held annually on 6 August, in honor of the Savior, the dedicant of the cathedral.
Post-Tridentine events A diocesan synod was held under Bishop Antonio Lombardo (1573 – 1579) in 1575. Bishop Bernardo Gascó (1579–1586) founded the diocesan clerical seminary in accordance with the decrees of the
Council of Trent in 1580. He held a diocesan synod in 1584. Cardinal Giovanni Domenico Spinola, bishop of Mazara (1636–1646), visited the diocese twice, in 1640 and in 1646. He held a diocesan synod in 1641, and published its decrees in a volume of 291 pages. Bishop Franciscus Maria Graffeo (1685–1695) held a diocesan synod in 1694. Bishop Bartolomeo Castelli (1695–1730) presided over a diocesan synod on 15 July 1698, and published the revised and amplified diocesan statutes. In 1670, the city of Mazara had approximately 9,000 inhabitants. In 1742, the town of Mazara had approximately 6000 citizens. On 8 June 1844, the
diocese of Trapani was established by
Pope Gregory XVI, with the bull "Ut Animarum Pastores." Six towns and their territories were withdrawn from the northern part of the diocese of Mazara. By a decree of the Consistorial Congregation of the Roman Curia, and with the approval of
Pope Pius XII, on 15 September 1950 the communities of Alcamo, Calatafimi, Castellammare del Golfo, and the territory of Borgo Fazio were removed from the diocese of Mazara and transferred to the diocese of Trapani. At the same time, the island of Pantelleria (Cossura) was transferred from Trapani to Mazara. By virtue of the Apostolic Letter, "Ianua Coeli", of 10 March 1962,
Pope John XXIII officially recognized the
Virgin Mary (under the title of Madonna del Paradiso), and Saints Vito, Modesto, and Crescentia as the patrons of the diocese of Mazara. ==Bishops of Mazara del Vallo ==