The Glosas Emilianenses (Spanish for "glosses of [the monastery of Saint] Millán/Emilianus") are glosses written in the 10th or 11th century to a 9th-century^[1] Latin codex called the Aemilianensis 60; the name Glosas Emilianenses is also sometimes applies to the entire codex. These marginalia are important as early attestations of both an Iberian Romance variety (similar to modern Spanish or Navarro-Aragonese) and of medieval Basque. The anonymous author of the glosses, presumed to be a monk at the monastery San Millán de Suso, wrote the glosses in three languages:

• A simplified version of Latin
• The medieval form of a Hispanic Romance language (traditionally regarded as Castilian or Old Spanish, but now most often classified as Navarro-Aragonese or a related dialect);
• Medieval Basque

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The latter two would have been the vernacular languages in the region surrounding the monastery, although there is a possibility that the author of the glosses was a newcomer in the area.^[2]

The literary critic and director of the Instituto Castellano y Leonés de la Lengua [es] Gonzalo Santonja has argued that the language of the Glosses is a "Latin language assaulted by a living language of the street which has crept into these writings".^[3]

The Glosses were formerly considered to include the first instances of early Spanish. However, in November 2010, the Real Academia Española declared that the first appearances of written Spanish can be found in the Cartularies of Valpuesta, IX century documents in an evolved Latin from the province of Burgos.^[3][4]

The codex is a compilation of several codices, including Verba seniorum, Passio martyrum Cosmae et Damiani, Sermones beati Augustini.^[1]

The codex is known as Aemilianensis 60 (Aemilianus is Latin for Emilian, "Millán" or "Emiliano" in modern Spanish) and was preserved in the monastery library at Yuso (the lower re-foundation of the monastery). Its significance was recognised in the early twentieth century when it was brought to the attention of the philologist Ramón Menéndez Pidal. The manuscript's current location since 1951^[1] is the Real Academia de la Historia in Madrid. The original place where it was produced is uncertain (M. C. Díaz y Díaz proposes the Pyrenees)^[1] but it is often assumed to be San Millán.

Some of the marginalia are grammar notes, others are additions and others, glosses. There is still some debate as to whether the Iberian Romance language of the glosses should be classed as an early form of Castilian or of Aragonese, although some recent studies show that most features belong indeed to the latter.^[5] It is not the only text to be difficult to classify: other texts traditionally assumed to be in Old Spanish, like the Kharjas, are proved to be in a different medieval Romance, Mozarabic, which happens to be classified along with Aragonese in a Pyrenean-Mozarabic group. Some scholars have proposed that it is anachronistic to classify such varieties of Ibero-Romance according to dialectal labels based on geographical particularism before the thirteenth century, leaving the Glosas to be understood as "in an unspecialized informal register of Ibero-Romance".^[6]

However, should the Romance language of the glosses be classified, San Millán de la Cogolla's former reputation as the "birthplace of the Spanish language" was important in its designation as a World Heritage Site ("cultural" type) in 1997.^[7]

Aemilianensis 60 has been publicized as the earliest known codex with inscriptions in Basque, though other codices are posited. ^{[citation needed]}

Only two of the glosses in Aemilianensis 60 (of a total of about one thousand) are actually in Basque.^[10] These short texts (only 6 words in total) can be seen on the 1974 plaque. However, it has been suggested that some of the Romance glosses reflect the influence of the Basque language, the implication being that their author was a fluent Basque-speaker.