The Duchess of Malfi is based on the true story of Giovanna d’Aragona and her brothers Lodovico d’Aragona, Cardinal of Santa Maria in Cosmedin, and Carlo d’Aragona, Marquis of Gerace. Gionvanna was married in 1490 when she was about twelve years old. Her husband became Duke of Amalfi in 1493 and died in 1498.
Giovanna ruled as Duchess and at some point secretly married Antonio Bologna, the master of her household. They had three children and managed to keep this secret from her brothers until at least 1509, and probably until closer to November 1510, when she took a sudden pilgrimage to Loreto. It became clear that this was only a pretext for escape when she continued to Ancona to meet Antonio.
In 1513, Duchess and her two youngest children were probably murdered in Malfi, and soon afterwards, Antonio was killed in Milan. Their oldest child survived. There is no historical evidence that the Duchess’s brothers were involved in these killings, but there is evidence the Duchess had long feared their retribution. Lodovico d’Aragona continued to enjoy power and success as cardinal, and died in Rome in 1519.
This is essentially all that lies in the historical record, and Webster probably used literary sources, likely including the firsthand account in Bandello’s novella Il Signor Antonio Bologna Sposa la Duchessa d’Amalfi, e Tutti due Sono Ammazzati, which told the story in more, likely fictionalized, detail that largely matches the plot points in Webster's play. Ultimately, what has made this play timeless is as much the author's pervasive worldview and unflinchingly grotesque theatricality as much as its plot, suggesting that like his contemporary Shakespeare, the source was but the starting point for a larger contemplation of human nature.