According to legend, Martim Moniz was a knight participating in the Christian invasion force, led by king Afonso I of Portugal, in the Siege of Lisbon, during the Reconquista.

The only two contemporary testimonies of the conquest of Lisbon from the Moors are the letters of the crusaders Osbern ("De expugnatione Lyxbonensi") and Arnulf, who, in their narratives, do not mention either this character or this episode.

Pedro Gomes Barbosa made the most recent critical synthesis of this subject, considering that the episode lacks tactical meaning since there was not really an assault on Lisbon, as the city surrendered.

[2] Although there are controversies in genealogical research, some authors believe that this person was in fact the son of Monio Osorez de Cabreira and Maria Nunes de Grijó, married to Teresa Afonso[3][4][5][6] (who some genealogists point out as an illegitimate daughter of D. Afonso Henriques and Elvira Gualter),[7][8] with whom he had three children: Genealogists point to another character with the name of Martim Moniz, who would have existed in 1149, married to Ouroana Rodrigues.

Son of Moninho Viegas, lord with possessions in Arouca, where Mór Martins was abbess, daughter (or descendant) of this Martim.