When Christian Menn stepped into the Big Dig fray in 1991, the plan for a new bridge across the Charles River was ominously called Scheme Z — a curling sprawl of ramps and lanes that critics likened to a poorly served plate of spaghetti.
Dr. Menn, a Swiss engineer and professor who was 91 when he died last Monday, took one look and thought: Why not try something elegant and attractive?
From the drawings he made while dining at the Harvard Faculty Club and while flying home to Switzerland emerged the design that became the Leonard P. Zakim Bunker Hill Memorial Bridge.
“Such a beautiful city should have a gateway,” he told the Globe in 2000, as the bridge he had sketched was taking shape.
Though Dr. Menn’s bridge designs dot his native country and the rest of Europe, the cable-stayed Zakim bridge towered over his other achievements.
“For me it was a great honor that I could elaborate the concept for the Charles River bridge,” he told the Harvard Gazette in 2001. “It was the biggest adventure in my professional life — not only because it is an interesting and original bridge, but I think also because it is in a very interesting, academic city.”
Dr. Menn’s death was reported by media outlets in Switzerland, which did not disclose a cause. He had lived in Chur, Switzerland, where he formerly ran an engineering company.
Though his Greater Boston connection centered principally on the Zakim bridge, that legacy will help define the city for scores of years to come. Carrying Interstate 93 across the Charles River before the highway dips into the Big Dig’s tunnels, the bridge is the most visible feature of the Central Artery/Tunnel Project — more than 180 feet wide and more than 1,400 feet long. Standing astride the lanes, two towers visually echo the Bunker Hill Monument, which drivers glimpse to the east.
“It’s not just a bridge,” said his friend Spiro Pollalis, a professor of design, technology, and management at the Harvard Graduate School of Design. “The bridge has become the symbol of Boston.”
It was Pollalis who invited Dr. Menn to speak at a workshop and conference at Harvard in 1991. Pollalis was part of the Bridge Design Review Committee, which was rethinking the Charles River crossing part of the Big Dig.
Scheme Z had drawn heavy criticism. That design called for a swirl of loop ramps that was roughly the size of Boston Common.
Many residents considered it “the ugliest monster that anyone had ever seen,” Charles Redmon, an architect on the review committee, recalled in a 2001 interview with the Harvard Gazette. “I don’t think anyone could find anywhere in the states a larger, more ungainly spaghetti mess of a roadway.”
Dr. Menn had a better idea for the committee. Driving into Boston from the north, he said, should be “like coming through a gateway, into the valley of the city. It should be very striking.”
Joining the Big Dig project as a consultant, Dr. Menn created a design in which aesthetics paid heed to environmental concerns, and beauty was built on a foundation of practicality.
In 1991, Dr. Menn told the Globe that “there should not be conflict between the bridge and its environment. That’s the first thing. Then the bridge should work as a structure. Ideally, there should be order and unity. Order, unity, and detail. A good designer has to pay attention to the detail.”
His success reimagining a better, more graceful design earned him a nickname: the Bridge Doctor.
“It’s very important that these and other structures not only be utilitarian, but that they look well,” he said. “I really think it’s a question of the well-being of the people.”
When finished, at a cost of slightly more than $100 million, the Zakim bridge was believed to be the widest bridge of its kind in the world. Yet under optimum conditions, when traffic flows smoothly outside of rush hours, the driving experience is fleeting — a car could cross the structure in less than 30 seconds.
“He put architectural form and engineering function into one,” then-governor Paul Cellucci said of Dr. Menn in November 2000. Cellucci predicted the bridge “will quickly become the signature of this city, if not of the entire Commonwealth.”
Dr. Menn was born in 1927 in Meiringen, a community in the Bern canton, or member state, of Switzerland. He received an engineering degree in 1950 from ETH Zurich, a science, engineering, mathematics, and technology university in Zurich. After working for a few years as an engineer with companies in Zurich and Bern, he became a research associate professor at ETH Zurich, from which he graduated in 1956 with a doctorate in science and technology.
Dr. Menn then worked as an engineer for a Paris company before moving to Chur, where for 15 years he ran an engineering company that was responsible for designing some 80 bridges, he said in his resume.
“He used to say, ‘Don’t think my bridges are beautiful. What makes them beautiful is the landscape of Switzerland,’ ” said Pollalis, who added with a chuckle: “I don’t believe he meant it.”
From 1971 until he retired in 1992, Dr. Menn was a professor of structural engineering and design at ETH Zurich. Afterward, he continued to work as a consultant.
“I find bridges more interesting than buildings,” he told Roads & Bridges magazine in 2000. “When you design bridges you are absolutely free in your design. When you are designing buildings, you always are collaborating with architects. And also, bridges are more attractive.”
Among those Dr. Menn worked with on the Zakim bridge project was architect Miguel Rosales, though Vijay Chandra, a consultant to Bechtel/Parsons Brinckerhoff, the Big Dig’s private project managers, told the Globe in 2002 that “Christian Menn is the conceptor of the whole bridge.”
Along with designing the Zakim bridge, Dr. Menn raised concerns about the structure after a 1999 visit. While photographing a beam on the bridge, he realized it had not been constructed properly and proceeded to write letters to Big Dig officials, alerting them to the flaw’s potential safety issues.
Eventually, the beam was repaired, but the experience slightly soured Dr. Menn’s relationship with his signature bridge. He didn’t attend the dedication in 2002, and he told the Globe at the time that the invitation he received was not personally addressed.
“Sometimes I have the impression that they still are not very happy that I detected absolutely by chance a weighty mistake and that I persistently insisted over two years to repair it,” he wrote in an e-mail from his Swiss home that October.
Information about Dr. Menn’s survivors and plans for a memorial service were not immediately available.
Dr. Menn “became an engineer but he could have been an architect. He was equally good as an architect and as an engineer,” said Pollalis, who worked with his friend and mentor on bridge designs.
In the 2001 Harvard Gazette interview, Dr. Menn said the experience of designing the Zakim bridge was “absolutely fantastic,” and added: “This is the most important bridge I have ever designed.”