August 26 is the feast day of Bergamo's patron, Saint Alexander, who is believed to have been a Roman centurion of the Theban legion imprisoned for his Christian beliefs.

The diploma specially mentions the church of S. Alessandro in Fara, which Bishop John converted from the Arian heresy to the Catholic faith.

[3] On 23 June 904 King Berengar I of Italy ordered Bishop Adelbertus and the citizens of Bergamo to rebuild the walls which had been destroyed during the incursion of the Hungarians.

In return for this service, the King confirmed and strengthened the Bishop's civil control over the city and area, even against his officials and feudal vassals.

[5] Arnulfus, the successor of Bishop Atto, was the son of Vido (Guido) of the area called Landriano, in the territory of Milan.

[6] His election was apparently quiet and canonical, since Pope Gregory VII refers to him in a letter of 21 June 1079 as having been reported to be receptive to papal counsel and obedient to his teaching: Arnulfum Berganebsus Ecclesiae electum, nostro libenter et consilio credere et praecepto oboedire.

He had chosen to support the schism of Archbishop Wibert of Ravenna, instigated by the Emperor Henry IV, and some German and north Italian bishops.

It confirmed the sentence of anathema which had been leveled by Pope Urban II against Wibert (Guibertus), Obertus of Brescia, Arnulfus of Bergamo, Gregory of Vercelli, and Anselm of Novara.

In 1101, the Canons of the Cathedral, led by the Archpriest Albertus de Zurlasco (Sorlasco)[12] (there being no Archdeacon in office), appealed to the new pope Paschal II, for protection.

[15] On 2 February 1106, another bull was received from Pope Paschal II, excommunicating Bishop Arnulfus and all the usurpers of the property of the Church of Bergamo.

[20] The Chapter met and appointed two Vicars Capitular instead of the customary one: Alessandro de' Clementi and Cipriano degli Alessandri.

[21] The delegation presented the electoral certificate to Canon Guglielmo in Avignon on 30 December 1309, who requested time to examine the situation and to consult with God.

vir D. Ciprianus Pergomensis electus et confirmatus (29 July 1310), point to a second election by the Cathedral Chapter and then papal confirmation.

All of these people were suspected of heresy and were being watched by the Roman Inquisition, whose head was Cardinal Gian Pietro Carafa.

[29] In the 1540s, the Inquisitor of Como and Bergamo was Fra Michele Ghislieri, O.P., whose attention was drawn to Sorzano by complaints from both civil and religious authorities.

[31] Impressed with Ghislieri's bravery and determination, Cardinal Carafa had him brought to Rome in 1551, and made him Comissary of the Holy Office of the Inquisition.

[32] On 22 June 1552, Pope Julius III suspended Bishop Sorzano from office, and appointed Niccolò Duranti as Administrator of the diocese of Bergamo.

[33] But while Julius III lived, Sorzano was protected by the Pope's hostility to the Inquisition and by the interest of the Republic of Venice.

[34] After the election of the Grand Inquisitor, Gian Pietro Carafa, as Pope Paul IV on 23 May 1555, the situation of Sorzano changed once again.

It was destroyed at the beginning of the 10th century, during the incursions of the Hungarians, and the remains of S. Alessandro were rescued and transferred to the church of S. Vincenzo, inside the city.

In 876, the Council of Pavia decreed in Canon X that the bishops should enclose the Canons: uti episcopi in civitatibus suis proximum ecclesiae claustrum instituant, in quo ipsi cum clero secundum canonicam regulam Deo militent, et sacerdotes suos ad hoc constringant, ut ecclesiam non relinquant et alibi habitare praesumant.

Bishop Federico Cornaro (1561–1577) and his Metropolitan, Archbishop Carlo Borromeo of Milan, both attended the last sessions of the Council of Trent.

[48] Immediately on his return to Bergamo, Cornaro held his own diocesan synod, on 4–5 September,[49] and announced the imposition of the tax authorized by the Council in its 23rd session (chapter 18), for the purpose of building a seminary for the diocese.

[63] In 2007, the diocese opened its 37th diocesan synod, a gathering dedicated to addressing problems and opportunities confronting parishes in the 21st century.

The Council of Trent, in its 23rd Session, meeting on 15 July 1563, issued a decree, the 18th chapter of which required that every diocese have a seminary for the training of clergy.

[64] In the diocesan synod of 4–5 September,[65] Bishop Fernando Cornaro announced the imposition of the tax authorized by the Council for the purpose of building a seminary for the diocese.

The bishop chose a location for the new seminary, at the Collegiate Church of San Matteo, which was administered by a Chapter composed of a Provost and four Canons.

There were two teachers, and the curriculum was extremely limited, grammar, catechism, Bible, patristic homilies, and works to develop the conscience.

In 1821, with a legacy of Canon Marco Celio Passi, it was possible to acquire several buildings near S. Maria in Monte Santo, which made possible the reunification of the entire student body in one residence.