What is the significance of the letters in "Roman Fever"?
The letter is at the heart of the deception that Mrs. Slade believed she perpetrated on Mrs. Ansley many years earlier when they were both in love with Delphin Slade.
One of these women married Delphin Slade, and one had a brief affair with him. One night when they were all in Rome, Mrs. Slade, Alida, knowing that Grace, Mrs. Ansley, was in love with her fiance decided to write Grace a letter, pretending to be Delphin arranging a meeting at the Colosseum.
What Mrs. Slade, Alida, didn't know was that when Grace got the letter she thought was from Delphin, she answered it and sent her reply to him.
He received the reply, they subsequently met at the Colosseum and had a brief affair. Mrs. Slade thought that she was going to discourage Mrs. Ansley from loving Delphin by arranging a phony meeting, where Grace would go to the Colosseum and wait and wait, with Delphin not showing up which would make Grace mad at him, and end her pursuit of him.
But Grace and Delphin actually met at the Colosseum, something that Mrs. Slade never knew until now, and Mrs. Ansley got pregnant with her daughter, Barbara, who Mrs. Slade discovers is the child of her late husband.
So the letter actually led to an affair which resulted in the birth of a child. Mrs. Slade thought she had discouraged Grace from loving Delphin Slade, when all she did was push her into his arms, at least briefly.