The architects of New York’s public library came to Philadelphia and built this amazing church | Inga Saffron

John Carrère and Thomas Hastings made their architectural reputation in the early 20th century with their design for the main branch of the New York Public Library on Fifth Avenue, an elegant marble palace with a long, soaring reading room and a pair of lions standing guard at the front steps.

Their firm, Carrère & Hastings, went on to design Henry Frick’s New York mansion, grand houses for the wealthy in Newport and Palm Beach, and a couple of stately government buildings in Washington, D.C. Yet, between those high-paying commissions, they managed to fit in a church for a small religious sect in West Philadelphia.

Today, most people know the distinctive neoclassical building at 40th and Walnut Streets as a performance venue called the Rotunda, but it started life in 1911 as a Christian Science church. Its evolution from the sacred to the profane tracks the changes in both the neighborhood and the religious group.

Founded by the writer and philosopher Mary Baker Eddy, the Church of Christ, Scientist (its formal name) had been in existence only three decades when members decided to establish a large church in Philadelphia. The sect, which believes that faith and prayer can heal physical ailments, had been expanding rapidly, especially among the middle-class professionals who were moving into West Philadelphia and who were drawn to its somewhat mystical teachings. They included the likes of Violet Oakley, the pioneering Philadelphia illustrator and muralist. Walnut Street, which was then lined with fine houses, was the perfect location for a statement church.

How the young Philadelphia congregation managed to snag one of the most sought-after firms of the day remains a bit of a mystery, according to a historic nomination written by Collette Kinane, a former student in historic preservation at Penn, and approved by the city in 2012. Carrère and Hastings were associated with the City Beautiful movement, which sought to transform cities with wide boulevards and stately classical buildings. Both men had studied at the famous École des Beaux-Arts in Paris and then landed jobs in the offices of McKim, Mead & White, the leading proponent of the classical style. With the success of the New York library, they became an architectural force in their own right.

But the most likely reason they were hired in Philadelphia is that they had just completed the first Christian Science church in New York at 96th Street. That building is conventional in form: a heavyset, rectangular English-style church with a pointed steeple. In contrast, their Philadelphia effort feels light and modern, even as it looks back to early Christian history.

The church’s most distinguishing feature, and the reason for its current name, is the large drum that houses the sanctuary and forms the heart of the building. That immense circular room is bisected by wings that, seen from above, clearly form a cross. Carrère and Hastings seem to have taken the Hagia Sophia in Istanbul, built in 537 as a Greek Orthodox cathedral, as the starting point for their design.

Yet this ancient form has been dressed in modern clothes. The cream masonry exterior lightens up the large structure, as does the red tile roof. A series of arched doorways mark the Walnut Street entrance. All the windows are decorated with a star-shaped lattice pattern. The combination of the buff facade and window tracery give this classical building an unusual delicacy.

It’s interesting that a new religion like Christian Science would take one of the most significant early Christian basilicas as its model. Perhaps this was a way for the new religion to suggest it was going back to first principles. The domed sanctuary is lit from above by a round oculus window. Sun pours in from large arched windows around the perimeter.

The building is set back slightly from Walnut Street, behind a brick-paved entry court where church members gathered before and after sermons. The brick pattern has an Arts and Crafts feel, as does some of the interior decoration, and it reprises the cross-in-a-circle plan of the church. Oakley designed a large, hand-wrought chandelier for the sanctuary.

The sect’s early success was not to last. Although the Church of Christ, Scientist does not publish numbers, it is believed that the sect had swelled to 300,000 members nationally by 1912. Today, that number is said to have fallen below 100,000.

The Philadelphia membership had dwindled dramatically by the 1980s. Around the same time, the once middle-class neighborhood was seeing many of its large houses converted into student apartments. Unable to maintain the building, which could accommodate 1,200 people in the sanctuary, church officials begged the University of Pennsylvania to take it off their hands. When the university finally acquired the building for $1 in 1995, the interior was badly worn.

Even in the building’s rundown condition, Penn was able to turn the old church into a performance venue. For many years, concerts and dance performances were held in the large sanctuary. But the city recently found lead paint there and ordered Penn to remove it. Penn shut down the sanctuary space. Events continue to be held in the back room, which once served as the church’s Sunday school.

Anne Papageorge, who oversees Penn’s facilities, said the university has been trying to secure a donor to help underwrite a renovation. Although there have been discussions about partnerships with the Wharton School and the Annenberg Center for the Performing Arts, none have materialized.

That’s a shame, because the Rotunda is the only work by Carrère and Hastings in Philadelphia (although they did design a mansion in Bryn Athyn). It is sad to see the magnificent sanctuary languish and remain inaccessible to the public. Temple University went through something similar with its original building, the Baptist Temple, but eventually transformed it into a spectacular modern performance space. Surely a university with Penn’s resources can do as much.