He then produced his scholarly investigation Horacio en España (1877), an analysis of Horace's translations in Spanish literature, with a prologue by the prominent critic Juan Valera.

The orthodoxy of this work is even more noticeable in the Historia de los heterodoxos españoles (1880–1886), and the writer was hailed as the champion of the Ultramontane party.

[4] As the Catholic Encyclopedia (1908–10) described his work, "Every page of his writings reveals a wealth of strong common sense, clear perception, and a vein of wonderful and ever varying erudition.

His work as an historian of Spanish literature was continued in his Historia de las ideas estéticas en España ("History of aesthetic ideas in Spain") (1883-1891), which are five volumes in which he explores, summarizes and reinterprets the existing bibliography on literary and artistic aesthetics at different times of the Spanish cultural tradition.

Another tremendous work was his Anthology of Castilian Lyric Poets (1890-1908), again 13 volumes devoted to medieval poetry (except the last one, dedicated to Juan Boscán Almogáver).

His work Historia de los heterodoxos españoles (1880–1882) is particularly famous and valued today especially where the Christian traditions of Spain are studied.

From the Middle Ages to the ending of the 19th century, he breaks down the work of all the thinkers and writers persecuted by the Spanish Catholic traditions, taking the perspective of Catholicism.

They explore, summarize, and reinterpret the existing bibliography about literary esthetics and artistics in distinct eras of the Spanish cultural tradition.