For centuries, the faithful have climbed up the Holy Stair’s 28 steps in Rome in prayer on their knees. But the popular devotion has been put on hold for an entire year, and the tall placard depicting the staircase is all the public can see as a team of Vatican restorers complete the final phase of a 20-year effort to repair the sanctuary of the Holy Stairs and clean its 18,300 square feet of frescoes.