This white marble altar dates back to 9 B.C. Though commissioned by the Senate to commemorate the Pax Romana brought about by Caesar Augustus, the structure was used as a stage for making sacrifices to the gods. Over the centuries, it was buried under silt from the Tiber but, not recovered, it is one of the most visited sites in the historical city center. In 2006, the museum opened to much fanfare. The mayor disliked architect Richard Meier’s modern design, but many view it as a stunning complement to the Ara Pacis, especially when the sun shines through the building’s glass walls and illuminates the altar just so. At times, the light has also shone on more contemporary creations, as was the case for ‘Valentino a Roma: 40 Years of Style.’