Mancini was one of the oldest families of Roman nobility. Their titles and fiefs were numerous: Duke of Nevers and Donzy, Prince of Vergagne and of the Holy Roman Empire with the treatment of Serene Highness, French Peer, Spanish Grandee, Marquis of Fusignano, Count of Montefortino, Viscount of Clamecy, Baron of Tardello, Tumminii and Ogliastro, Lord of Claye-Souilly, Roman noble and Venetian patrician. They were knights of the Order of the Golden Fleece, of the Order of the Holy Spirit, of the Order of Saint Michael, of the Sovereign Order of Saint John of Jerusalem and many more. The humanist Marco Antonio Altieri (1457–1537) includes them in Li Nuptiali, an important collection of news about Rome in the 16th century. The family was granted the Honneurs de la Cour of France.
Of Roman origin, the family has thousand-year roots in Italy, and traditionally asserts a line of descent from the gens Hostilia, whose line took the surname Mancinus and whose Lucius Hostilius Mancinus was Consul in 608 "ab Urbe condita", all the way back to Lucius Hostilius Mancinus who was consul in 145 BC and a commander of the Roman fleet during the Third Punic War.
The Mancini family was called de Lucij (or simply Lucij) in Rome for the fishes on its coat of arms. Many of the members were "Conservatori all'Urbe". The first known member of the family is Lucio Mancini who lived in 990. In the centuries the family had various lines that thrived with nobility everywhere, particularly at Fermo where the first memories go back to 1160 giving to the city Priori, Consoli, Gonfalonieri and Dottori, but the most important are:
The family coat of arms had inspired the heraldry of the French commune of Liernais.