[1] His main work, for which he is chiefly remembered, was the posthumously printed Dacia Preistorică (1913), with a preface contributed by C. I. Istrati; a facsimile edition was published in 2002 by Editura Arhetip, Bucharest.
In 1878 he received a commission from the Romanian Academy to research and collect historical documents in the libraries and archives of the Hungarian Kingdom (Budapest) and in Transylvania at Cluj, Alba Iulia and Brașov.
Along the route, he visited the Academy of Agram, where he studied manuscripts regarding the Vlach population settled in the valley of the Kupa (in present-day Croatia); in Istria, he collected material in local villages where the Istro-Romanian language was spoken.
He also contributed a collection of folklore (Vechi cîntece și tradiții populare românești: texte poetice din răspunsurile la "Chestionarul istoric", published in 1893–1897).
Among his earliest critics was Titu Maiorescu, leader of the conservative literary society known as Junimea, who strongly reacted against amateurism and Romantic nationalist discourse in the works of Romanian intellectuals of his day.
In 1893, writing to geographer Simion Mehedinți, Maiorescu spoke against what he defined as "phantasmagoria" in the works of Densușianu, Bogdan Petriceicu Hasdeu, and Alexandru Dimitrie Xenopol.
[6] Part of Densușianu's thesis was adopted by several official historians during the late years of Nicolae Ceaușescu's communist regime, serving as inspiration for a new discourse, one autarkic and nationalist in tone.
[7] Vasile Pârvan stated: "Nicolae Densusianu wrote his fantastic novel Prehistoric Dacia, full of mythology and absurd philology, which at its appearance (posthumously: 1913) aroused an admiration and a boundless enthusiasm among lay Romanians for archaeology".
"[11] Eugen Ciurtin stated "a minimal contact with the bibliography of the subject leaves one hopeless: nobody reads him any longer" (meaning no serious scholar has written peer-reviewed articles about Densușianu's Dacia Preistorică for a long time).