The Franklin Institute in Philadelphia is displaying a Lego representation of St. Peter’s Basilica and St. Peter’s Square. A priest in Pennsylvania built it with about half a million of the plastic bricks. (Matt Rourke/AP)

Philadelphia’s science museum was playing host to a blockbuster exhibit of Lego sculptures and preparing to unveil a huge display of treasures from the Vatican for Pope Francis’s upcoming visit when administrators got a curious inquiry: Would they like to see a model of the Vatican that a priest had built — entirely of Legos?

“It’s amazing,” said Larry Dubinski, president of the Franklin Institute, where the plastic-brick structure is on view in downtown Philadelphia. “People are in awe.”

The Reverend Bob Simon spent about 10 months constructing a miniature St. Peter’s Basilica out of a half-million Legos. His architectural feat includes a Lego pope on a balcony overlooking the crowd in St. Peter’s Square, which is made of about 44,000 Lego pieces resembling cobblestones.

A colorful cast of Lego characters populates the square, including a nun with a selfie stick and a bespectacled figurine of Simon. All told, the display measures 14 feet by 6 feet and weighs about 100 pounds.

“It was daunting,” Simon said. “It was an exercise in patience, and I was thrilled with the way everything came out.”

From a balcony at the basilica, a Lego figure of the pope looks out over a crowd in the plaza. (Matt Rourke/AP)

Simon said he built his first crude Lego model of the Roman Catholic Church’s headquarters when he was in seventh grade. Today, he serves as pastor at St. Catherine of Siena church in Moscow, Pennsylvania, about 125 miles north of Philadelphia. He has visited the real Vatican five times.

To create the model, Simon used an image from a book cover as a guide. The hardest part was crafting the round basilica dome from square bricks, he said. Although he looked for hints by watching YouTube videos, “I hardly understood what I was watching,” he said.

“I’m also not really great at math,” he added, “so I was daunted by that as well.”

Yet he persevered. Using Lego life preservers to replicate the dome’s windows — one of many ways he repurposed various shapes — he delicately built the structure without glue.

Denise Brownell, visiting the museum from Phoenix, Arizona, was impressed. “It’s just such a perfect replica of the real thing,” Brownell said. “It’s just awesome.”

Simon started the project a year ago in an empty room in the house he shares with other priests. He finished in time to bring it to this summer’s BrickFair, a Lego convention in Northern Virginia, where it received many awards. A friend suggested that the Franklin Institute might be interested.

Simon’s creation is being displayed alongside “The Art of the Brick,” an exhibit of Lego sculptures, and “Vatican Splendors,” which includes art, ceremonial clothing and religious items from the Vatican.

One of the figures in the crowd is a nun with a selfie stick. (Matt Rourke/AP)

There are no plans for Pope Francis to see the Lego Vatican while he’s in Philadelphia this weekend. But Simon hopes to see the pope: He will participate in the papal Mass on Saturday.