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It took architect James Ingo Freed and his crew nine years to design and build the new $738 million Ronald Reagan Building and International Trade Center—not counting another 11 years of planning before that. So I am mildly shocked when Washington architectural historian Pamela Scott tells me she had nine weeks to mount Completing the Federal Triangle: The Ronald Reagan Building and International Trade Center, an exhibition on the epic project at the National Building Museum.

“Nine weeks?” I ask Scott dubiously.

“Nine weeks from the day it opened,” she replies. The show opened last week. “It had to be done very quickly, which wasn’t enough time. I don’t feel I understand the building adequately.”

Scott is being modest. If anybody can tell the tale of Federal Triangle in a hurry, it is she, who has been studying Washington, keystone by quoin, since 1976. Scott, who is 53, came here that year from Cornell to teach at the school’s Washington outpost and took a summer job cataloging 30,000 architectural drawings at the National Archives. Then she edited the papers of 19th-century Washington architect Robert Mills at the Smithsonian, and, later, those of Pierre Charles L’Enfant for the L’Enfant Forum. In 1993, Scott and co-author Antoinette J. Lee, also a historian, published Buildings of the District of Columbia, an indispensable volume that is part of the Buildings of the United States series being produced by the Society of Architectural Historians and Oxford University Press.

The Reagan building exhibit was rushed because the museum had another show drop out at the last minute. Nonetheless, Scott managed to document much of the process of planning Federal Triangle, most of which was completed after a decade of construction in 1938. In particular, the guest curator focused on the events following the federal government’s 1989 design competition for what would become the Reagan building; the competition models are on view alongside the story of Freed’s winning scheme.

On top of the tight deadline, Scott says, she also had trouble finding stuff to show: Few of the architects who competed for the project had saved their original drawings properly. “1989 is ancient history to architects today,” she observes. And for all the time the 3-million-square-foot Reagan building took to complete, it was built on an accelerated schedule, which meant that the design changed constantly, and full-blown detail drawings of many of its most important features were never completed by Freed’s firm.

“There were no pretty drawings of the rotunda,” Scott laments. There were, she says, only a few sketches available of the stunning, 125-foot space at the heart of the complex. “It’s very discouraging what it says for the future of American history. It’s almost easier finding out about 19th-century buildings. We’ve really thrown out the 20th century.”—Bradford McKee

Completing the Federal Triangle: The Ronald Reagan Building and International Trade Center runs through September 27 at the National Building Museum.