Ashley Wilkes alludes to the House of Borgia, an aristocratic family that gained prominence and notoriety during the Italian Renaissance, after Rhett Butler makes an appearance at Twelve Oaks during a large party: 

All the ladies except Mrs. Tarleton moved out of the back yard, leaving the shade of oaks and arbor to the men [...] Ashley strolled over to where Scarlett and Charles sat, a thoughtful and amused smile on his face. “Arrogant devil, isn’t he?” he observed, looking after Butler. “He looks like one of the Borgias.”

Scarlett thought quickly but could remember no family in the County or Atlanta or Savannah by that name. “I don’t know them. Is he kin to them? Who are they?”

An odd look came over Charles’ face, incredulity and shame struggling with love.

Earlier, Rhett spoke pessimistically and mockingly about the South's preparations for war, a speech that is received with hostility by the other party attendees. As Rhett retreats into the library and the crowd disperses, Ashley describes Rhett as an "arrogant devil" and states that "He looks like one of the Borgias." Here, he alludes to the House of Borgia, a noble family that gained both fame and infamy during the Italian Renaissance for its political prominence and associations with crime and immorality. Ashley's allusion, then, emphasizes Rhett's status as an outsider in North Georgia, as he appears to the locals to be from a different time and culture. Scarlett does not catch the reference and mistakenly assumes that the Borgias are a family living nearby in Georgia, an error that underscores her own lack of interest in history and art and the gap between her interests and those of the learned Ashley.