This windswept outcropping, peering over the Atlantic, was a Gilded Age haven where the wealthy built mansions known by their names, not addresses: The Elms, Marble House and, most famous of all, The Breakers, built by Cornelius Vanderbilt II as a family retreat and a Renaissance-inspired monument to their success.

Newport has cared deeply about appearances ever since.

So when large steel beams rose high in the air between the city’s most storied thoroughfares, framing a mansion that will have an unusual, many-sided shape and a flat roof, neighborhood residents and observers were aghast.

“This looks like a 30-foot-tall Martian spaceship landing on the Newport skyline,” said John Peixinho, a former chairman of the Historic District Commission.

Ross Cann, an architect whose apartment in a grand house overlooks the new home, said, “We’re just baffled by why somebody would want to inflict themselves on Newport in such a way as this.”