“This magnificent piece could have been used over a mantelpiece or as a pier mirror. A fashionable young couple in New York debated this very topic in an 1845 novel, Evelyn: A Tale of Domestic Life by Anna Cora Mowatt, when they “had an animated conversation … concerning the arrangement of a large mirror which they had just purchased” for their handsome house. “‘We must have it placed over the mantel-piece,’ said Mr. Merritt. ‘I bought it exactly to fit there.’ ‘No, no,’ returned Evelyn. ‘I do not like glasses over mantel-pieces; it must be placed between the windows.’” After much discussion, the besotted husband “acknowledged himself conquered,” and his wife put the mirror where she wanted it.”
Classical Reflections: Recent Gifts from Richard T. Button, by Margaret Highland, Mansion Musings, July 27, 2018
Maybe this is more about marriage than decor.
“trumeau. Noun. (plural trumeaux) (architecture) The pillar or center post supporting the lintel in the middle of a doorway, especially in a church. A trumeau mirror.”