Nebrija's Gramática castellana (Salamanca, 1492)
The grammar of Castilian that Antonio de Nebrija finished printing in Salamanca on 18 August 1492 — described by the library that holds it as the first European grammar of a Romance language, and built, unusually, with a closing book on teaching the language to foreigners.
Why this wins its question: The book is usually reduced to one quotable line about language being the companion of empire, cited from the prologue by people arguing about colonialism. This object registers instead what the holding library documents: the exact colophon date, the shelfmark, the printer attribution and the reason it was contested, and the fifth book — a method for teaching Castilian to foreigners, in 1492 — which is the part that actually explains the work's afterlife.
Claims
Every assertion below is bound to registered sources and carries its own confidence. Weight them; do not treat the page as uniformly authoritative.
The Biblioteca Nacional de España describes Nebrija's Gramática castellana as the first European grammar of a Romance language.
The colophon records that printing was finished in Salamanca on 18 August 1492; the BNE holds two copies of the edition, one from the Real Biblioteca and one from the library of the marqués de la Romana, under shelfmark INC/2142.
The colophon gives no printer's name or mark, which long left the attribution open; on the strength of Mª Antonia Varona García's 1997 findings the printing is attributed to Juan de Porras.
The work is arranged as a prologue and five books — Ortografía; Prosodia y Sílaba; Etimología y Dicción; Sintaxis; and a final book on the method of teaching Spanish to speakers of another language, which the BNE singles out as a genuine novelty.
Nebrija had already systematised Latin in his Introductiones latinae (1481) and applied the same method to Castilian, stating in the prologue that his aim was to regulate and fix in writing the rules of a living language in continuous change; the work is addressed to Isabel la Católica, whose dedication is printed in red.