Eljas is also the name of the river that flows through the locality. Castaño Fernández (125) has brought together the different hypotheses and we see that the name has many graphic variants, since, in addition to As Ellas in Fala, Erjas or Erges in Portuguese, we find Elga, Elgas, Ergas, Erga, Erje, Heljas, Herjas and Herjes – the last three mentioned by Menéndez Pidal -, as well as Elia, Elias. Menéndez Pidal himself (LI) believes that the etym may be *Herlias, analogous to Herly, from a Celtic Herliacum. DOELP (s. v. Erges) resorts to a pre-Roman name with the root Elg(u) or Erg(u); and there are also those who speak of a possible Latin ergastulum ‘prison of servants in the countryside’, as well as of an illas ecclesias ‘the churches’.

Cited bibliography: 

-Castaño Fernández, Antonio M. Los nombres de Extremadura. Estudios de toponimia extremeña. Mérida: Editora Regional de Extremadura, 2004.

-DOELP = Machado, José Pedro. Dicionário onomástico etimológico da língua portuguesa. Lisboa: Livros Horizonte, 2003, 3ª ed.

-Menéndez Pidal, Ramón. “Dos problemas iniciales relativos a los romances hispánicos.” En Manuel Alvar dir. Enciclopedia Lingüística Hispánica. Madrid: CSIC, 1960. Tomo I, XXVII-CXXXVIII