ROME, ITALY—For the past six months, workers wearing waterproof gear have been cleaning the first five of the Colosseum’s 80 arcades. The travertine is soaked with water for one to four hours, and then scrubbed with soft-bristled brushes to remove 2,000 years’ worth of grime and pollution. “We had the chance to examine past restorations closely and see how the philosophy of shoring up the structure has evolved through the centuries,” Rossella Rea, director of the Colosseum, told The Wall Street Journal. Scholars expect that as the scaffolding is moved to other parts of the monument, they will discover frescoes, stucco work, inscriptions, and graffiti.