While Navy pilot Michael Christian was being held in the infamous prison complex known as the Hanoi Hilton after he was shot down over North Vietnam in 1967, he made a small American flag by sewing some ragged bits of red and white cloth inside his blue prison garb.

Every day, Christian would hang his shirt on the wall and he and his cellmates, including future senator John McCain, would pledge allegiance to the makeshift flag. When guards finally discovered it, they beat Christian. Back in his cell, while recovering from serious injuries, Christian began making a replacement flag with his original bamboo needle.

"This is a man who literally put his life on the line" for the flag, said Marc Leepson, a Middleburg author who served in Vietnam around the same time as Christian and has thought about that act often. "After all, it's cloth. It's a piece of cloth. But obviously it's much more than a piece of cloth. That got me thinking, 'What more is behind this?' "

Those thoughts led him to write the recently published "Flag: An American Biography," which explores the evolution in the culture and meaning of the Stars and Stripes, and includes an account of Christian's flag making.

The book traces the life story of the flag, from its creation in 1777 -- not at the hands of Betsy Ross -- to its emergence as a popular symbol of Unionist patriotism during the Civil War, its burning by protesters during the Vietnam War and its use as a symbol of a united nation at war against terrorism after Sept. 11, 2001.

"Americans have a unique and special feeling for our flag," Leepson wrote in the introduction to his book. "And that's putting it mildly. . . . No country in the world can match the intensity of the American citizenry's attachment to the fifty-star, thirteen-stripe Stars and Stripes, which is as familiar an icon as any that has existed in the nation's history."

Nowhere else, Leepson said, do people display their flag as often, as passionately and as ubiquitously as do Americans do, especially on the Fourth of July -- when it flies from front porches and its image appears on everything from bikinis and bandannas to paper plates.

Leepson and flag scholars say the flag is an important and accessible unifying symbol for a country of immigrants with no common religion, monarchy, race or mythology. While Mexicans adorn household shrines and handbags with the images of the Virgin of Guadalupe and Britons raise their glasses to Queen Elizabeth II, Americans revere and display their flag.

The national anthem is a hymn of praise to the flag. There is an official U.S. Flag Code. And a Flag Day, June 14, the day Leepson's book was published.

Visitors to this country are sometimes "amazed to see so many U.S. flags flying," said Joyce Doody, executive director of the National Flag Foundation, a nonprofit organization based in Pittsburgh that promotes patriotism and respect for the flag. In some countries, she said, "it's more a symbol of the government, not the people."

Whitney Smith, director of the Flag Research Center in Winchester, Mass., and author of 26 books about flags, agreed. He said that when considering the degree to which countries are attached to their flags, it helps to try to answer one key question: Who owns the flag, the people or the government?

"There is a spectrum," Smith said, between authoritarian regimes where the government tells people when and how to use the flag, and the United States, where people feel free to use it in all kinds of ways. The lines of distinction are sometimes blurred, he said, even in this country.

Particularly during times of war, there have been laws governing how people should use the flag. During World War I, Congress made it illegal to manufacture, sell or advertise goods decorated with the flag, and several states outlawed defacing or defiling the flag, the book says. A constitutional amendment that would give Congress the power to ban flag burning was approved by the House of Representatives this month and for the first time stands a chance of passing in the Senate, congressional leaders have said, after which it would be sent to the states for ratification. The House has passed the measure four times before.

For the most part, Smith said, "there is a broad and deep attachment" to the flag in America, "because people use it in their own special ways," including artistic displays or as a personal accessory. Although some people dislike -- and the flag code forbids -- use of the flag for commercial purposes or personal attire, the practice is widespread and the code is not legally enforceable.

In some countries, the flag may be a formality, something to show the world that you are a country, but not a source of deep feeling, Smith said. In Afghanistan, for example, which is made up of many ethnic groups, "their allegiances are to their people and languages and self-interests and regions," Smith said.

Smith, a political scientist, founded the field of flag research more than 40 years ago and called it vexillology. He coined the term from the Latin word vexillum, which means "little sail" or flag. The field is still young and made up mostly of people who work on it in their spare time, so there have been relatively few serious comparative studies about flags.

An informal survey was conducted recently by self-proclaimed flag geek Peter J. Orenski of New Milford, Conn., who sells flags and flag memorabilia. He decided to test the theory that nowhere were people as crazy about their flag as the United States.

Orenski posted his survey questions on www.crwflags.com, a Glen Burnie-based Web site devoted to flags of all types, including those of other nations, and received 157 responses from 47 countries. According to his results, published in the Flag Bulletin, the Flag Research Center's bimonthly publication, flags seem to be more popular and more widely used in other countries than U.S. flag scholars have thought.

In Canada, the maple leaf was adopted as the national flag's symbol emblem as recently as 1965, decades after the country achieved independence from Britain. The government distributed millions of flags to promote the new symbol. A combination of wanting to develop a unique identity and compete with the flag-waving next door has led to an increase in patriotic display in Canada, Orenski said.

Orenski said he thinks that personal flag use is more common in countries with histories of a struggle for independence or national identity. Flags were also pervasive under communist regimes, but in a more controlled way.

"A flag was what I carried in a parade on the first of May," said Orenski, who grew up in Romania under communism. "Flags were an instrument of propaganda."

Smith cited Haiti as a country with a flag tradition that rivals that of the United States. After a long struggle against the French, Haiti's nearly half-million slaves revolted, and in 1804 the country became the first black-led republic. The new leaders cut the white stripe out of the French flag to signal that they were no longer a colony. The blue stripe represents black and mulatto people, and the red stripe represents the blood they shed for their independence. Later they added a coat of arms.

In the United States, the mass appeal of the flag is rooted in the struggle not to become a nation but to remain one, Leepson said.

"Before the Civil War, it was almost unheard of for individuals to fly the flag," Leepson said. It was flown mainly over federal facilities and forts, and on ships and commercial vessels. In his research, Leepson looked at newspaper accounts after the fall of Fort Sumter to Confederate forces, the first engagement of the Civil War.

"It almost read like what happened after September 11," he said. The next day, "the flag was in front of every house and store. People put [flags] in their hats and on their horses."

The relationship was sealed.

Marc Leepson's book recounts the U.S. flag's story, from its creation in 1777 to its emergence as a popular symbol of Unionist patriotism during the Civil War, its burning by protesters during the Vietnam War and its use as a symbol of a united nation at war against terrorism after Sept. 11, 2001.