Ottavio Bertotti Scamozzi’s arch in Vicenza; published in “Descrizione dell’arco trionfale,” 1758.

We know, at least somewhat, how Paris looked in 1662: huts for the poor, massive palaces for the rich, a few stunning churches. It’s harder to know how Paris appeared then when it was decked out for a royal wedding or coronation.

That’s because the décor for special occasions — triumphal arches, massive lighting fixtures, amphitheaters, wedding houses — didn’t last long. The structures, not intended to be permanent, weren’t built of long-lasting materials. With no cameras around to show what such structures looked like, you had to be at the right place at the right time.

“Some of these structures were really grand. It’s amazing to think they were only up for a day, maybe a week, and then disappeared,” says Yuri Long, a circulation technician in the National Gallery of Art Library. Long curated the NGA’s “Fleeting Structures of Early Modern Europe,” a new exhibit of etchings from rare books depicting temporary additions to European cityscapes. The books, dating from about 1550 to 1800, were culled from the library’s collection of hundreds.

Published to document festivals, the hardcovers — some of which are nearly 2 feet wide when open — are all today’s scholars have to help them understand certain events.

Still, “you have to wonder how accurate these books are,” Long says. Many were printed long before an event in order to promote it. Others weren’t published until a decade afterward. “In a lot of cases, the books were a political tool, just like the festival was often a political tool to further the aims of whoever was putting it together. They’re basically trying to show off.”

The images’ dubious authenticity adds to their intrigue. As Long says, “It raises the question: What is the relationship between the book and the actual event?”

Ottavio Bertotti Scamozzi’s arch in Vicenza; published in “Descrizione dell’arco trionfale,” 1758.
Artist Cristoforo Dall’Acqua documented a triumphal arch (above) created by Ottavio Bertotti Scamozzi for a religious festival in Vicenza in 1758. Scamozzi later executed his own drawing of the arch in 1780, and there were obvious differences between his own depiction and Dall’Acqua’s etching, including discrepancies between the placement and content of friezes on the structure.

Peter Mayer’s engraving in “Beschreibung der Feyrlichkeiten…,” Freiburg, 1770.
Artist Peter Mayer depicted a temporary lighting display added to the Freiburg cathedral in honor of Marie Antoinette’s 1770 visit to the city (left). Antoinette was a 14-year-old bride en route from Vienna to Versailles for her wedding to Louis XVI when the city and several private houses were lit up for the evening.

National Gallery of Art, 4th Street and Constitution Avenue NW; through July 29, free; 202-737-4215. (Archives)