Nineteen metres beneath the cobblestones of Vicolo del Puttarello sits a residential insula abandoned in the fifth century, its ground floor flooded when the Aqua Virgo aqueduct ruptured during the Gothic sieges. The water never receded. For fifteen centuries, silt accumulated above limestone thresholds and mosaic floors until 1999, when contractors excavating a cinema foundation broke through into a vaulted chamber still holding the mineral-stained bones of the ancient water system. The site now known as Vicus Caprarius preserves the intersection of imperial hydraulic engineering and domestic life, offering one of the few public access points to the subterranean conduits that fed Rome's eleven aqueducts. The Aqua Virgo, commissioned by Marcus Agrippa in 19 BCE, remains the only classical aqueduct still delivering water to central Rome. Its name derives from the legend of a young girl who led thirsty soldiers to a spring fourteen miles east of the city. The conduit carried twenty-four million gallons daily, supplying the Baths of Agrippa and later the Trevi Fountain itself. The Trevi Fountain underground aqueduct tour reveals the engineering precision behind this flow: arched galleries lined with waterproof signinum concrete, inspection shafts at measured intervals, and sedimentation basins that allowed particulates to settle before water reached the city's fountains. The exposed channels at Vicus Caprarius show erosion patterns consistent with two millennia of hydraulic force. Above the aqueduct foundations, the excavation uncovered a multi-story apartment block occupied from the Augustan period through late antiquity. Frescoes depict garden scenes and theatrical masks. Terra sigillata pottery shards bear makers' stamps from Gaulish and North African workshops, evidence of Mediterranean trade networks. A well shaft descends eleven metres, its stonework blackened by centuries of rope friction. The building's abandonment coincides with the decline of aqueduct maintenance during the Gothic Wars, when Vitiges cut the water supply in 537 CE. Archaeological tours through the site interpret stratigraphy and construction techniques, connecting the material record to historical events documented in Procopius and Frontinus. The tour route follows catwalks suspended above the excavation floor, preserving the fragile archaeology while allowing visitors to observe the layered chronology. Lighting reveals the junction where the aqueduct channel intersects the insula's foundation walls. Interpretive panels document the excavation process and the conservation challenges posed by fluctuating groundwater levels. The site operates as a municipal museum, with entrance managed separately from the fountain above, though both monuments share the same hydraulic history that shaped the urban fabric of Rome.