Not far from Piazza del Popolo, the Roman cisterns are entered through a door in Via degli Aceti, a steep and evocative alley in the historical centre with characteristic brick paving. The large underground complex of the great Roman cisterns, datable to the end of the 1 st Century B.C. and unique in Italy for its area in square metres, is made up of 30 intercommunicating rooms, laid out in three parallel rows. They were part of a complex system involving a well-organized aqueduct which started with spring water and distributed it throughout the town. The imposing size and excellent condition add charm to an underground journey through Roman building techniques and hydraulic engineering. Inside we can observe traces of impermeable concrete, the brick lining of the partition walls, the imprints of the boards used to make the ceilings of the single rooms, the cleaning platforms, the aeration wells, the inlet and outlet pipes.