<p>A modern name given to the subterranean waterway flowing out of the valley between the *Collis Hortulorum and *Quirinal, where stood the *Horti Sallustiani. In the pre-Augustan period, it probably fed into the <i>palus Caprae</i>, a large marsh that stood to the W of the *Saepta Iulia. By the time Agrippa built his *Thermae, the swamp had been drained, and the waters that fed into it were channeled into formal drainage systems. Traces of the Aqua Sallustiana’s channels are shown running beneath the modern Via del Tritone on Lanciani’s <i>Forma Urbis</i> (<i>FUR</i> pl. 15), and another section of it was discovered in 1913 flowing under Montecitorio (Richardson). This waterway was once thought to be the *Petronia Amnis (Lanciani), an identification now overturned on the grounds that it lies too far to the N to create a meaningful boundary between the city and the *Campus Martius (Hülsen; cf. Festus 296). The ancient name of the “Aqua Sallustiana” is as yet unknown.</p><p>Coarelli claims that the “Aqua Sallustiana” split into two branches near the point where it intersected the *Aqua Virgo, and that one of these branches determined the orientation of the angled side of a triangular *Delta structure S of the Temple of *Isis Campensis. It is unlikely, however, that the course of a drain or sewer would be divided in such a way, and it is not clear in any case why the underground channel of a watercourse other than the Petronia Amnis would have impacted the shape of urban development in this way. Richardson plausibly argues that the “Aqua Sallustiana” simply continued to flow due W, emptying into the Tiber somewhere near the modern Ponte Umberto I.</p>