From his youth, Stefano Borgia manifested an aptitude for historical research and a taste for relics of ancient civilizations, a line in which he succeeded so well that, at the age of nineteen, he was received into the Academy of Cortona.
He founded a museum in Velletri, in which, during his whole life, he gathered coins and manuscripts, especially Coptic, and which may be considered his major undertaking and achievement.
Such was his passion for antiquities that he is known to have sold his jewels and precious earthenware in order to secure the coveted treasures and have the description of them printed.
After the proclamation of the Republic, he was arrested (1798), but quickly released, whereupon he immediately resumed his studies and work of collecting; soon afterwards he joined Pius VI in Valence, Drôme, and endeavoured to have this pontiff send to Asia and Africa a body of missionaries who would preach the Gospel and gather various monuments.
Before the partition of the manuscripts was made the scholar and convert, Georg Zoëga, wrote a complete and accurate description of them in his posthumous work Catologus Codicum Copticorum manuscriptorum qui in Museo Borgiano Velitris adservantur (Rome, 1810).