In this paper some newly discovered cippi of the Anio Vetus and the Marcia relating to the Augustan restoration of 11–4 BC, which were found in the section between the sources and S. Maria di Cavamonte (Via Prenestina), are described. Other cippi are re-evaluated and for each of the aqueducts an up-to-date catalogue is given. It is important to note that the distance between the cippi was not always based on the iugero of 240 pedes (that is 70 metres), there being many exceptions, in some cases the distance being greater (particularly in more winding hilly sections), in others less. Also the shafts for cleaning and repairs are not regularly spaced at 70 metre intervals, often being 35–37 metres apart. The cippi, placed along the edge of the ground reserved for the aqueduct channel, not always corresponding to the shafts, are given a progressive number starting from Rome. This served to identify (with the help of plans (formae)) the section of the aqueduct requiring maintenance.
Given that the distance between the cippi varies, it is not possible to calculate the length of the aqueducts (or of particular sections) by multiplying the serial number by 240 pedes. Therefore we should reject the corrections made to Frontinus' figure for the length of the Anio Vetus of 43 miles, as these are based on this method (the figures suggested being 53, 55 and 63). In addition the aqueduct starts at the 29th mile of the Via Valeria, that is 9–10 miles upstream of Tivoli, not 20 (a misreading of the text of Frontinus). There follows a discussion of the length of the other three aqueducts of the Anio valley (Claudia, Anio novus, Marcia).
In Appendix l a small quarry pit from which the tufo cippi of the Anio vetus may have been extracted is described. In Appendix 2 a map of 1866 is presented, showing the location of some sections of the Marcia and the Claudia along the Via Valeria.