ST. LOUIS, Missouri (AP) -- When architect Eero Saarinen was creating the design of this city's famed Gateway Arch, he constructed his first model out of pipe cleaners.A long way from its humble beginnings, the shimmering steel Arch celebrated its 40th anniversary Friday.The original builders autographed posters of the monument as they answered questions from visitors, and an exhibit on Saarinen opened in the museum beneath the Arch. Book signings were held for an anniversary publication, "The Gateway Arch, An Architectural Dream."Schoolchildren who had never seen the Arch came for the first time."Well, 40 years," said a silver-haired Susan Saarinen of Golden, Colorado, daughter of the late architect, who last saw the Arch at age 20. "Not very much time compared with the pyramids, but the last time I was here I had blonde hair and computer-aided design didn't exist."The idea for a memorial in St. Louis began in 1933 with lawyer Luther Ely Smith, who was looking for a way to beautify the city's run-down riverfront, the first glimpse many visitors got of St. Louis.Although work was done to secure and clear 90 acres, the idea for a memorial was not revitalized until two years after World War II.Saarinen created a design that would mark President Thomas Jefferson's role in the nation's westward expansion (Jefferson signed the Louisiana Purchase in 1803, which doubled the size of the United States) and honor the 19th century migration of hundreds of thousands of people to the West at a time when St. Louis was the last major city before the frontier.Saarinen recounted in a 1948 newspaper article how he came up with the Arch's design by thinking about how earlier memorials to "our three greatest men" -- Jefferson, George Washington and Abraham Lincoln -- each had a distinct geometric shape.He began to envision a dome with a design more open than the Jefferson Memorial in Washington, perhaps one that touched the ground at three points."We tried it in a very crude way; the only things we could find to make it with were some pipe cleaners. But three legs did not seem to fit in the plan, so we tried it with two legs, like a big arch."The design competition that Saarinen's team entered in 1947-48 had 172 submissions, including one from his father, the well-known architect Eliel Saarinen. Eero was just 38 and his father's reputation far surpassed his own at the time.When a Saarinen advanced in the competition, Eliel received a telegram congratulating him and the family broke out a bottle of champagne."Two hours later the family received a phone call from an embarrassed competition official," Eero's daughter, Susan Saarinen, Susan Saarinen said in the new book. It was young Eero, and not his father, who had a chance to win. "Eliel, a very proud father, broke out a second bottle of champagne" to toast his son.Eero Saarinen died in 1961, before the Arch's construction from 1963 to 1965. The new exhibit runs through July 16.Copyright 2005 The Associated Press. All rights reserved.This material may not be published, broadcast, rewritten, or redistributed.