Three places of worship occupy the same vertical footprint at Via Labicana 95, each built directly atop its predecessor across seventeen centuries. The fourth-century basilica you enter from street level conceals a first-century Roman house and a third-century Mithraic temple twenty feet below, themselves resting on foundations from the Great Fire of 64 CE. Irish Dominicans began systematic excavation in 1857, draining groundwater from the Lateran aqueduct that had flooded the lower chambers for nine hundred years. San Clemente underground tickets grant access to this archaeological vertical where early Christian frescoes, pagan altars, and imperial-era masonry coexist in a single descent. The stratification is Rome's most legible chronicle of religious succession. The ground-floor basilica preserves a twelfth-century apse mosaic showing the Tree of Life — its spiraling acanthus vines frame thirty meters of gold tessera work commissioned under Pope Paschal II. One level down, the fourth-century lower basilica retains ninth-century frescoes depicting the Miracle of San Clemente, narrative panels that predate Giotto by four centuries. The legend of Sisinnius — a pagan husband cursing in vernacular Latin while his Christian wife prays — appears in what scholars recognize as the earliest written Italian, predating Dante's Florentine by three hundred years. Descending to the Mithraic level reveals a second-century sanctuary carved from a Roman apartment block. The triclinium benches flank a stone altar showing Mithras slaying the cosmic bull, the zodiac relief intact above the dedication slab. Archaeologists identified the complex as an insula — a multi-story rental property typical of imperial Rome's dense urban fabric — repurposed for mystery cult worship during the Antonine dynasty. The adjacent first-century rooms contain tufa-block walls and herringbone brick that survived Nero's fire, their original floor levels now submerged beneath the water table that feeds a constant trickle audible throughout the excavation. Conservation engineers maintain dehumidifiers and drainage pumps around the clock. The 10 EUR entry supports this preservation infrastructure, funding the sump systems that prevent the Cloaca Maxima from reclaiming the chambers. San Clemente underground tickets tours include expert interpretation of the stratigraphy, though self-guided visits allow independent navigation of the illuminated corridors. The site opens Monday through Saturday from 09:00, closing at 12:30 for the midday break and reopening at 14:00. Sunday access begins at noon. The excavations maintain controlled visitor flow to preserve fresco pigments degraded by humidity and modern breath. Booking windows fill earliest on weekday mornings when cruise-ship groups have not yet arrived from Civitavecchia.