During his time as bishop, Atto was known for his devotion to the welfare of the people in his diocese, both temporal and spiritual, and the vigour with which he attacked ecclesial corruption.
His major compositions include Polypticum, a treatise on the morality of Italy in the day; De pressuris ecclesiasticis, an essay regarding ecclesiastical authority; and the Capitulare, a collection of canon law from his area, including some of the False Decretals, augmented by his own additions of ecclesiastic law.
[11] Atto did not agree with Lothar's unjust means of ruling, but was unsuccessful in making any real changes, as he could only council the young king.
[16] He claimed public entertainment was fabricated by the infamous “demons” Liberus and Venus as a device to incite depravity.
[28] It was said that once restored to its original purpose, the cloth used to bear the dead would be tainted and pollute the altar and Mass it was meant to serve.
[32] Atto inexplicably decided to warn against the consultation of magicians and seers in all ranks of the clergy during his time as Bishop of Vercelli, although there is little evidence that it was still widely regarded as a problem.
[35] Alongside his larger works, Atto also wrote The Exposition on the Epistles of Saint Paul, a commentary that would have been used to educate the clergymen of Vercelli.
[36] A small collection of Atto's Epistolae, or letters, has been preserved, probably compiled from the codices of Vercelli and the Vatican library.
[39] It is sometimes referred to by its full name, De pressuris eclesiasticis libellus, meaning “Book on the Pressures of the Church.”[40] It contains discourse regarding the jurisdiction of the Church and its law and argues against the maltreatment of laypeople.
[42] Sometimes referred to as Perpendiculum, meaning “perpendicular,” “line,” or “plummet,” this work seems to have been completed near the end of Atto's life, perhaps in his last months.
[46] It satirizes the political struggles between princes and nobility in the time period, and shows Atto's distaste and pessimism about the age in which he lived.
Linda Fowler-Magerl calls it the long-winded Capitula canonum excerptarum de diversis conciliis decretalibus statutis atque epistolis congruentium ad forense iudicium tempore domini Attonis episcopi, which translates roughly to “Excerpt chapters of canons about the different decretal statute councils and the corresponding letters to the legal judgment in the time of the lord Bishop Atto.”[48] W. C. Korfmacher uses the shortened Canones statutaque Vercellensis Ecclesiae, roughly meaning “Canons and Statutes of the Church of Vercelli.”[49] Paul Collins prefers the abbreviated Capitulare, simply meaning “capitulary.”[50] It is clear in their writing, however, that Collins, Korfmacher, and Fowler-Magerl reference the same work, namely Atto's compilation of and additions to ecclesiastic law.
[58] As always, Atto devoted some of his efforts in canon law towards the greater good of his congregation: his collection included the requirement of clerics to bury their parishioners, and to be able to teach them both reading and writing.