Moscow ? St. Basil’s Cathedral, Russia’s most recognizable landmark with its swirling, multicolored onion domes, is on shaky ground.

Over the years, the rumble of tanks during Soviet-era military parades, the construction of underground infrastructure and the excess decibels of outdoor rock concerts have taken their toll on the cathedral’s foundations.

Now, with scaffolding set to come off next month after a three-year restoration of the aboveground part of the cathedral, experts say intensive work to strengthen the foundation may be necessary to keep the building standing.

If nothing is done, “the church will gradually fall into ruin,” said Natalia Almazova, whose company, Kreal, conducted a comprehensive engineering study of St. Basil’s for the government. “It won’t fall down tomorrow, but if we don’t take these measures, in 100 years we could lose it.”

The effects of time on the cathedral are visible with the naked eye: deep cracks in the inside walls and a tilting bell tower. The 20th century took the worst toll, but earlier influences, such as fires and the paving of Red Square with cobblestones, also caused problems, Almazova said.

Nevertheless, Almazova — who calls herself “a doctor who treats buildings” — was optimistic. “It’s deformed, but it has adapted to this deformation.”

What’s needed, among other things, is to reinforce the foundation of the retaining wall and install a new drainage system so that puddles don’t form around the cathedral, she said.

Culture Ministry experts are studying Kreal’s conclusions and recommendations. A decision is expected in September, and, if approved, the work could start next summer.

Russian media have raised fears that plans to convert a historic building next door at 5 Red Square into a retail, office and hotel complex with an underground parking garage could further shake the 4 1/2-century-old cathedral’s foundations.

“Absolutely, this is a colossal cause for concern,” Almazova said. However, she said modern engineering tools allowed planners to evaluate the effect the construction would have on St. Basil’s, and draw up plans accordingly.

St. Basil's Cathedral, near Moscow's Red Square, is half covered by scaffolding for restoration. Modern developments have taken their toll on the 500-year-old cathedral's foundations.

Igor Mitichkin, deputy director of the State Historical Museum, of which St. Basil’s is a part, said he did not believe the construction work would affect the cathedral.

What he is upset about is the recent practice of holding concerts on Vasilyevsky Spusk, the cobblestone slope in back of St. Basil’s, and, in some cases, on Red Square itself. Mitichkin says he is certain the vibrations are damaging all the historic buildings on the square, adjacent to the Kremlin.

Adding insult to injury, in his view, organizers of Paul McCartney’s May concert on Red Square demanded the scaffolding around St. Basil’s come down so that the ex-Beatle could have the famed cathedral as a backdrop. The process of dismantling and rebuilding the scaffolding took two weeks, Mitichkin said.

The scaffolding and green mesh are scheduled to come off for good Aug. 17, revealing cupolas with an almost shockingly bright paint job, instead of the more muted tones Muscovites have grown accustomed to. The cathedral’s last sprucing-up was timed for the 1980 Moscow Olympics –a rush job, according to Mitichkin.

Almazova said she was confident the famed cathedral would continue to dazzle tourists for another 500 years, thanks to the mind-boggling precision of its 16th-century builders.

“I’m a modern person. I understand physics, I understand construction mechanics, I understand calculations,” she said. “I don’t understand how five centuries ago … they could achieve this.”