Costigan, Ethna Mary Byrne- (1904–91), academic and writer, was born 24 May 1904 at Upper Leeson Street, Dublin, the eldest daughter of Thomas Joseph Byrne (qv), chief architect to the Office of Public Works, and Mary Ellen Byrne (née Scott) of Drogheda, Co. Louth. As a young child she was sent to live with relatives in Italy, and received her early education at Les Dames de Scion convent in Rome. On returning to Dublin she lived alternately with her aunts and grandfather in Dartmouth Square, and with her parents in Ballyboden and later Rathgar. She attended Loreto Hall in St Stephen's Green and studied at UCD, graduating with a first-class BA in modern languages in 1925, and a first-class MA in French in 1927. She went on to the Sorbonne in Paris, where she gained her doctorate; her thesis, entitled ‘Bourdaloue moraliste’, was subsequently published by Beauchesne.
Following the retirement of Professor Mary Ryan (qv) in 1939, she was appointed professor of Romance languages at UCC. She remained in this post until 1969, during which time she inaugurated a refresher course for French teachers. Among her academic publications are her studies of Molière's Le bourgeois gentilhomme, Corneille's Horace, and Racine's Athalie. Her Irish translation of Silvio Pellico's Le mie prigioni (1833) is in the Pellico Museum in Turin, and the Italian Institute published her Irish version of a number of Salvatore Quasimodo's poems. With her associate, Dr Piero Calì, she founded the Dante Alighieri Society in Cork, of which she served as president from 1956 to 1969. On retiring from the professorship at Cork she lectured part-time on Italian philology and medieval texts at TCD. She served on the Irish national committee of UNESCO, and was twice selected to represent Ireland at the biennial conference in Paris. She also served as honorary secretary of the Celtic Congress. In recognition of her work in promoting Italian language and culture in Ireland the Italian government made her a grand official (grand' ufficiale) of the Italian Order of Merit in 1960.
An accomplished embroiderer, her work has been exhibited in the USA under the auspices of the Embroiderers' Guild. In 1941 she married the Egyptologist and linguist George Costigan (d. October 1951), with whom she had one daughter. Under the pseudonym ‘Ethna Bee Cee’ she published her memoirs, Ethna Mary twice (1989), describing her childhood in Rome and Dublin. In later years she remained active, and at the age of eighty delivered a lecture on Lady Sydney Morgan (qv) to the Old Dublin Society (published in the Dublin Historical Record, xxxviii, Dec. 1984). She died 12 January 1991 at her home in Palmerstown Villas, Rathmines, Dublin.