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. [Illustration: FIG. 12.9 Aqueducts near Capannelle, reconstruction (painting). (Deutsches Museum, Munich)]