Twenty-six centuries of water engineering lie beneath the cobblestones at Vicolo del Puttarello, where the Vicus Caprarius archaeological zone preserves the subterranean chambers of Rome's Aqua Virgo aqueduct. Completed in 19 BCE by Marcus Agrippa to supply his public baths, the aqueduct still carries spring water from Salone—fourteen miles east of the city—into the Trevi Fountain above. The underground site was discovered in 1999 during routine building renovations, revealing not only the ancient waterworks but also the remains of a luxury Imperial-era apartment complex, complete with frescoed walls, mosaic floors, and a private cistern. Today the site functions as a working archaeological laboratory. Visitors descend nine meters below street level into climate-controlled galleries where the original aqueduct channel runs alongside stratified residential ruins spanning the first through fourth centuries CE. The Aqua Virgo remains operational—its clear flow audible in the exposed conduit—making this one of the few places in Rome where ancient infrastructure still performs its original function. The apartment remains include a service corridor, storage rooms, and a private water distribution system that tapped directly into the public aqueduct, a privilege reserved for the wealthiest residents. The site takes its name from the Vicus Caprarius, a Roman street referenced in ancient property records. Among the recovered artifacts are over eight hundred coins spanning five centuries, African red slip pottery from Carthaginian trade routes, and fragments of a colossal marble statue likely depicting a member of the Severan dynasty. The coin hoard provides a precise chronology of the building's occupation and eventual abandonment during the Gothic sieges of the sixth century, when Rome's population collapsed and maintenance of the aqueduct system became impossible. Conservation work continues on-site. Archaeologists have stabilized the frescoes using techniques developed for Pompeii, and ongoing excavation in the eastern gallery suggests the residential complex extended beneath the modern Palazzo Poli. Trevi Fountain underground tickets provide access to these working excavations, where stratigraphic layers remain visible in the gallery walls and interpretive panels explain the engineering principles behind gravity-fed aqueduct distribution. The site operates Tuesday through Sunday with limited daily capacity to protect the fragile environment, and advance reservation is standard practice during peak visitation months.