Sister Virginia Maria (born Marianna de Leyva y Marino; December 4, 1575 – January 17, 1650) was an Italian nun.

She gave birth to two children fathered by a local aristocrat, and had connived in the murder of another nun to cover up the affair.

She was the daughter of Martìno de Leyva and Virginia Maria Marino, widow of Ercole Pio Count of Sassuolo, and great granddaughter of Antonio de Leyva, who inherited the title to a County from Charles V. Virginia was the daughter and direct heir of one of the richest man in Milan, the banker Tommaso Marino.

Martino was the second son of Luis de Leyva, Prince of Ascoli, who was an army captain and first Spanish governor of Milan.After the death of her mother Virginia in 1576, the infant Marianna was entered into a long trial for her inheritance, which was eventually not resolved in her favor.

The scandal was caused by her love affair with the count Giovanni Paolo Osio, who had previously been accused of murder.

The meetings between them were frequent and were organized with the complicity of other nuns and a priest named Paolo Arrigone, a close friend of Osio.

Alma subsequently lived with her father, Count Osio, who legally acknowledged her as his illegitimate daughter two years later in 1605.

Marianna defended herself by claiming loss of free-will, asserting that diabolic forces had exercised on her an irresistible impulse.

In the verdict, on October 18, 1608, Sister Virginia was sentenced to be walled-in for 13 years in the Home of Santa Valeria[clarification needed].

It is described through a "flashbacks" technique, along with particular combinations of nouns and adjectives which suggest a hidden anguished secret in the nun's previous life.

[10] Through her back-story we learn that her religious vows didn't stop her physical urges, and she had a relationship with an evil aristocrat, Egidio, who pushed her to become his accomplice in the murder of a nun: this is her tormenting secret.

[11] The principal female characters, Agnese and Lucia, meet Gertrude (The Nun of Monza) while escaping from the villain Don Rodrigo.

Her decision is difficult for her, emphasizing Manzoni's view of her as a weak tool of evil, unable to resist threats and temptations, but basically not cruel.

The preliminary novel of The Betrothed, entitled "Fermo and Lucia", dedicated six chapters to the story of the nun from Monza, which Manzoni then reduced to only two.

[13] In a letter addressed to his friend Cesare Cantù, Manzoni states that he is unable to identify the nun of Monza because he is not in possession of documentation from the Borromeo household.

Like the nun of Monza, Gertrude is an abbess, had a saint life, and in the 16th century she is depicted in a painting chasing away the rats that are the main vehicles carrying the plague.