Helen Langdon, Caravaggio: A Life
(New York: Farrar, Straus and Giroux, 1998), p. 134, with note on p. 402:
In 1593, for example, a young married woman, Leonora Palelli, who lived near the Piazza dei Santissimi Apostoli, denounced Decio and Onorio for making a disturbance in the streets, beneath her windows — 'singing with lutes and guitars abusive songs in the manner of famous insults' (libelli famosi), and making such a racket that all the neighbours had come out.6
6 S. Corradini, 'Nuove e false notizie sulla presenza del Caravaggio in Roma', in S. Macioce (ed.), Michelangelo Merisi da Caravaggio: La Vita attraverso i Documenti (Rome, 1995), p. 73. Obscene lyrics were part of the usual weaponry of scorned young men; E. Cohen, in 'Honor and Gender in the Streets of Early Modern Rome', Journal of Interdisciplinary History, xxii, 4, 1992, p. 613, tells the story of a young prostitute, Aurelia, woken by the delicate harmonies of lute and guitar, accompanied by the lyric 'Oh little whore, now comes the summer / Prepare your ass for your lover'.
Andrew Graham-Dixon, Caravaggio: A Life Sacred and Profane
(New York: W.W. Norton & Company, 2011), p. 254:
On 28 August , Baglione lodged a complaint with the Governor of Rome about some libelli famosi, or 'famous libels'. The accused were Onorio Longhi, Caravaggio, Orazio Gentileschi and the hapless Filippo Trisegni.
It seems to me that "famous insults" and "famous libels" are misleading translations of the phrase libelli famosi
. The phrase, which occurs in both Latin and Italian, would be better translated as "defamatory writings."