Apostate priest, born Viterbo, Italy, 1803. He was suspended by ecclesiastical authorities for immorality, and later imprisoned by the pontifical government for revolutionary agitation. He gave anti-Catholic lectures in London; exposed by J. H. Newman (afterwards cardinal) he brought a libel action in 1852, in which Newman was fined £100, owing to the anti-Catholic prejudices of the judges. Achilli afterwards became utterly discredited (Ward, "Life of Newman"), and the incident caused a revulsion in favor of Newman.