Luca pushes his head into the sewer, inhales, and grins. "It doesn't smell so bad in the cloaca today," he says, dropping himself feet first into a dark hole in the middle of the Forum of Nerva. Despite his optimism, the blackness emits sickening aroma: a mélange of urine, diesel, mud, and rotting rat carcasses. In short, it smells just as you'd expect a 2,500-year-old continuously used sewer to smell. Below in the dark, tuff-vaulted cavern itself, things aren't much better. As Luca wades through water the color of army fatigues, stepping over garments of temples and discarded travertine washed down over the ages, a diorama of modern life floats past: cigarette butts, plastic bags, plastic lighters, a baby pacifier, and a disturbingly large about of stringy, gray stuff that looks like toilet paper, although raw sewage isn't supposed to be flowing through here. At one turn, Luca points out a broken amphora, perhaps 2,000 years old, lying in the mud next to a broken Peroni beer bottle, perhaps a week old. Together they provide a striking testament to how long people have been throwing their garbage into the gutter of this city.