The middle part of Egeria's writing survived and was copied in the Codex Aretinus, which was written at Monte Cassino in the 11th century, while the beginning and end are lost. This Codex Aretinus was discovered in 1884 by the Italian scholar Gian Francesco Gamurrini, in a monastic library in Arezzo. Recently, Prof. Jesús Alturo has identified two new fragments from one manuscript circa 900 in Caroline script.
Gamurrini published the Latin text and theorised the author was Saint Sylvia of Aquitaine. In 1903 Marius Férotin claimed the author is one Aetheria or Egeria, known from a letter written by the 7th century Galician monk Valerio of Bierzo. He dated her pilgrimage to about 381–384, during the reign of Theodosius I.:vii f. Férotin believed she was from Gallaecia, but in 1909 Karl Meister disputed Férotin's theory about the date of Egeria's pilgrimage and her identity. Meister argues that her language shows no evidence of Spanish dialect, but rather, suggests that she may have been from one of the well known religious houses of 6th century Gaul; under this theory, her pilgrimage would have taken place in the first half of the reign of Justinian (r. 527–565).:viii f. John Bernard has noted that certain details of Egeria's account that would support a later date—two churches mentioned in the Breviarium and Peregrinatio Theodosii (both circa 530)—are absent from Egeria's otherwise detailed description of Jerusalem and thus confirm the 4th century dating.:xiv Most scholars favor the 4th century date.
It is through Valerio's letter that we first see the name Aetheria or Egeria, and have much of the biographical information. He praises Egeria and identifies her as a nun, perhaps because she addresses her account to her "sorores" (Latin for "sisters") at home. However, others (including Hagith Sivan, 1988) have pointed out that during Egeria's time it was common to address fellow lay Christians as "sisters" and "brothers." It is possible that Egeria used the term to address her Christian acquaintances. Valerio may also have believed her to be a nun because she went on such a pilgrimage, although lay women of the time are known to have engaged in such religious tourism. Egeria's ability to make a long and expensive journey by herself, her numerous acquaintances and attentive guides in the places she visited, and her education indicate her middle or upper class wealthy background.:xi In his letter to Egeria, Valerio mentioned the shores of the "Western sea" or "Ocean" from which Egeria was sprung, which suggests he was writing about a person travelling from the Roman Gallaecia, but Meister believes that her reference to the river Rhone supports his theory of Gaulish origin.:viii f.
Egeria set down her observations in a letter now called Itinerarium Egeriae ("Travels of Egeria"). It is sometimes also called Peregrinatio Aetheriae ("Pilgrimage of Aetheria") or Peregrinatio ad Loca Sancta ("Pilgrimage to the Holy Lands") or some other combination. It is the earliest extant graphic account of a Christian pilgrimage. The text has numerous lacunae.
Philologists have studied Egeria's letter, which contains a wealth of information about the evolution of Latin in late antiquity into the "Proto-Romance" language, from which the medieval and modern family of Romance languages later emerged.