Fig. 12.8 Rome and environs, map showing aqueducts. (V. Scramuzza and P. MacKendrick, The Ancient World, Fig. 33a)
We owe our knowledge of Rome’s aqueducts to three people, one ancient and two modern: Sextus Julius Frontinus, water commissioner under Trajan, whose book on aqueducts survives, Dr. Thomas Ashby, former Director of the British School at Rome, and Miss Esther B. Van Deman of the American Academy. For over thirty years, before modernity removed the traces, this devoted pair tramped the rough country between Tivoli and Rome, plotting the courses of the major aqueducts. Their definitive work is well-nigh as monumental as the aqueducts themselves. Together they explored the mazy course of the aqueduct channels, above ground and below, along crumbling cliffs and the edge of deep gorges, over walls, through briers, across turnip fields, in the cellars of farm-houses and wine-shops. They climbed and waded; Ashby explored downshafts “with the aid of several companions and a climber’s rope,” and when they were through, the courses and the building history especially of Rome’s four major aqueducts, the Anio Vetus (272–269 B.C.), the Marcia (144 B.C.), the Claudia (A.D. 47), and the Anio Novus (A.D. 52)—all repeatedly repaired—were better known than they had been since Frontinus’ day, and fellow archaeologists were in a position to draw from their detailed pioneer work important conclusions about Roman hydraulic engineering and about Roman culture.
Following Frontinus’ indications, Ashby and Miss Van Deman found the sources of the four great aqueducts at over 1000 feet above sea level, in springs or lakes in the upper reaches of the Anio valley, near Subiaco, Mandela, and Vicovaro. The airline distance of the sources from Rome varies from twenty-four to twenty-seven miles, but to follow the contours the aqueducts took a circuitous course, so that their actual length is from forty-three to sixty-two miles. Though the modern reader associates Roman aqueducts with the magnificent lines of arches ([Fig. 12.9]) stretching across a once-empty Campagna near Rome, the fact is that well under a third of a Roman aqueduct’s course was normally carried on arches: the rest was tunnel or side-hill channel. The reason for this was in part economy, in part strategic considerations: an aqueduct below ground is harder for an enemy to find and cut. When the Goths finally did cut the aqueducts in the sixth century A.D., the seven hills of Rome became, and remained for centuries, unfit for civilized habitation.
Fig. 12.9 Aqueducts near Capannelle, reconstruction (painting).
(Deutsches Museum, Munich)
The four aqueducts, Ashby and Miss Van Deman found, followed the course of the Anio fairly closely from their source to just below Tivoli, where, having lost half their altitude, they turned south along the shoulder of the hills to Gallicano. In this stretch, at Ponte Lupo, the Aqua Marcia crosses a gorge on a bridge that would test the mettle of the most seasoned archaeologist, for it epitomizes Roman constructional history in stone and concrete for almost nine centuries. After Gallicano the intrepid pair traced the aqueducts’ course westward, where, by a system of tunnels, inverted siphons (the Romans knew that water would rise to its own level), and side-hill channels they cross the broken gorges of the Campagna to a point south of Capannelle racetrack, six miles from Rome, whence they proceed on the famous arches to the Porta Maggiore. From reservoirs in the city the water was distributed in lead pipes (one, of Hadrianic date, has walls three inches thick, and weighs eighty-eight pounds per running foot), with a strict priority, first to public basins and fountains (the Aqua Julia alone supplied 1200 of these), next to baths (extensions of the Marcia supplied those of both Caracalla and Diocletian), then to private houses. Surplus was used for flushing the sewers. Attempts were made to control the priorities by running the pipes for private use only from the highest levels of the reservoirs, but Frontinus complains bitterly of illegal tapping.
In the Gallicano-Capannelle stretch special archaeological ingenuity is required, first to find the channels, and then to decide which belongs to which aqueduct. Where the channels have entirely disappeared, through the disintegrating action of floods, earthquake, tree roots, or plowing, the course can be defined by plotting the occurrence of heaps of calcium carbonate on the ground. This is the aqueduct deposit. Roman water is extremely hard, and the heaps mark where once there were downshafts (putei) for inspection and cleaning the channels, which without such maintenance would soon have become completely blocked with deposit. Frontinus says the downshafts occurred regularly every 240 feet, and Dr. Ashby found many at just this interval.
For distinguishing one aqueduct from another there are many criteria. The first is construction materials. The earliest aqueducts are built of cut stone, the latest of brick. Miss Van Deman was famous for her precise dating of building materials; she was the only archaeologist in Rome who could date a brick by the taste of the mortar. A second criterion is quality of workmanship. The Claudia, for example, is notoriously jerry-built: where abutments are found which should be solid, but are instead one block thick, filled in with earth behind, that channel belongs to the Aqua Claudia. A third criterion is mineral deposits. Thus the Marcia was famous for its purity; the crystalline lime deposits were quarried in the Middle Ages, polished, and used to decorate altars. The Anio Novus, on the other hand, is distinguished by a singularly foul deposit. A fourth criterion is directness of course: the older the aqueduct the more sinuously it runs; a channel found meandering by itself along the contours is likely to be that of the Anio Vetus.