CHARLESTON, S.C. — Witold Rybczynski , an architecture critic, author and emeritus professor of urbanism at the University of Pennsylvania , was sitting in the lobby of a chain hotel here, trying to peg the elusive charm of this city. After all, as Mr. Rybczynski wrote in his new book, “Charleston Fancy” (Yale University Press), the city of 130,000 people has no world-famous buildings, no grand boulevards and few public squares of any attractiveness. And yet, nearly 7.2 million tourists visited last year.

“I think a big part of it is this preserved Colonial town,” Mr. Rybczynski said, noting that after the Civil War, Charleston and its beautiful old houses and buildings “just kind of went into mothballs.”

Later, the historic downtown was saved from the worst of urban renewal and real-estate speculation because Charlestonians were very conservative, Mr. Rybczynski said, and because the history of the city and the history of families is all mixed together.

“Saving an old building was really saving your family’s old building,” he said. “That’s why they were the first city to become aware of historic preservation and to have zoning based on history.”