Marion Elizabeth Blake, Ancient Roman Construction in Italy from the Prehistoric Period to Augustus (Washington, D.C.: Carnegie Institution of Washington, 1947), pp. 159-161.

Works of Agrippa

To carry out Julius Caesar's grandiose scheme for a new city at a higher level, a renovation of the entire system of sewers became necessary. Dionysius describes it as a truly colossal work draining every street of the city, though he erroneously attributes it to the early kings, as does Pliny also. Augustus seems to have entrusted this monumental task to Agrippa. Since drainage had to be provided for surface water, it involved the paving of fountain areas and the regulating of the course of the Tiber within a new embankment. It is difficult to tell how much of the latter was completed by Agrippa, as the terminal stones were not set up until 8 B.C., four years after his death. If he built the emissarium of the Cloaca Maxima (pl. 15, fig. 3), as Dr. Van Deman believed, he doubtless reorganized the bank at that point, re-using such of the Grotta Oscura blocks of an earlier embankment as he could, and adding some of Gabine stone. The embankment has been so thoroughly systematized in modern times that it is difficult to judge of the ancient Roman work. Agrippa's new bridge would presuppose a regulation of the bank in its vicinity. When he was aedile in 33 B.C., Agrippa personally inspected the sewers, but in order properly to appraise his contribution, it would be necessary to examine every foot still extant in much the same way that Dr. Van Deman has analyzed the aqueducts. The erroneous belief that the Cloaca Maxima went back to the period of the kings has invalidated most of the chronology proposed for Rome's ancient sewer systems. It was divided into three main parts: the Campus Martius system, the Cloaca Maxima and its branches, and the Circus Maximus system. The northern basin has left a few remains along Corso Umberto I from San Carlo to Palazzo Sciarra, along Via del Seminario to the Pantheon, and from Piazza Mattei to the Tiber. The ancient engineers took advantage of such drainage as was furnished by the Petronia Amnis. Where the walls and vaults are both of Gabine stone, it is probable that we are dealing with Agrippan work. The southern basin had eight tributaries flowing into a single channel and emptying, through it, into the Tiber about a hundred meters below the outlet of the Cloaca Maxima. There is, as we shall see, some reason for believing that Agrippa in this section substituted a vault of Gabine stone for an earlier one of the same tufa as that in the walls.

More is known of the Cloaca Maxima. It started near the southeast corner of the Forum of Augustus and passed in an irregular course westward to the Argiletum, receiving the contents of a number of branch sewers as it went. From its beginning to Via Alessandrina both walls and vaults were of great blocks of Gabine stone (3-4 m. x 1 m. x 1 m.), and the floor was of selce. This sounds like Agrippan work. Beyond Via Alessandrina, the upper part of the walls had been restored in brick-faced concrete with a vault of selce concrete. This may be Augustan. It was 3.20 m. wide and 4.20 m. high. Traces of an earlier section with walls and vault of cappellaccio may still be seen running obliquely beneath the pavement level of the first shop to the west of the west passage leading into the Basilica Aemilia. Dr. Van Deman was inclined to associate this with the Sullan rebuilding of 78 B.C. In any case, it was widened and repaired with travertine and tufa in preparation for the restoration of 14 B.C. Its barrel vault of the same materials was only slightly lower than the floor of the basilica. At the "Porticus of Gaius and Lucius," however, it changed its course to correspond to the orientation of the porticus, and passed directly across to join the new channel near the Shrine of Venus Cloacina. This part was entirely of concrete of the same variety as that used in the foundation of the porticus, with which it was clearly contemporaneous. Meanwhile, the main body of the sewer was carried under the Argiletum to the street which bounded the Forum on the north. It then proceeded eastward to a point just beyond the Shrine of Venus Cloacina, where it joined the other branch before crossing the Forum. Its wad and vault were also of tufa and travertine. An important branch coming from the Tullianum skirted the front steps of the Curia Julia in such a way as to show that it was later -- that is to say, built after 29 B.C. -- and so gives support to the conjecture that both this and the section of the main cloaca into which it emptied were constructed in connection with the restoration of the Basilica Aemilia after the fire of 14 B.C. Its masonry consisted of stone walls and a concrete vault. Presumably, the branch from the Sacra Via joined the main cloaca as it turned to cross the Forum. None of the part under the Forum itself seems to have come to light. The section under the steps of the Basilica Julia was entirely of concrete and certainly belongs to the period when the basilica was built. At this point the main cloaca received contributions from various sources. A branch from the Velia passed in front of the Temple of Castor. Another at the rear of the temple was Augustan at its lower level. Yet a third, of fine Anio masonry at 12.50 m.a.s.l., may have drained the late Republican or Augustan Lacus Iuturnae. The Cloaca Maxima next passed through the Velabrum to the Tiber. This part is largely of travertine with restorations of the Imperial period, though Narducci shows a fine section uncovered near Via dei Fienili which is of Gabine stone, constructed of great blocks (2.5 m. x 8o cm.-1 m. x 8o cm.) laid on stretchers so that wider blocks alternate with narrower ones. There are three courses in the walls and seven voussoirs in the vault. A sewer west of the Cloaca Maxima in the Forum area ran under the Clivus Capitolinus and through the Vicus Iugarius at least as far as Santa Maria della Consolazione, where it probably joined the main cloaca. The construction was entirely of tufa (variety not specified) including floor and flat roof, at least in the upper part of the course which Dr. Van Deman ascribed tentatively to the Augustan period. The lower part had been rebuilt in Imperial brickwork, and it revealed branches in both the original masonry and the restoration. The arch of three concentric rings of voussoirs which formed the mouth of the entire system (pl. 15, fig. 3) is well known to every tourist, but its date has been bitterly contested among scholars. The Gabine stone in it may point to Agrippa. In any case, the Cloaca Maxima suffered modification at the construction of practically every important Augustan building along its course, and each modification used a different technique. Most of the remains belong to the Augustan epoch with Imperial restoration. Its top seems to have settled the Augustan level for much of the Forum and Velabrum, and its rather erratic course is due to a regard for Augustan edifices. The construction appears to be normally in opus quadratum of Gabine stone in the Agrippan restoration, and of Anio tufa or travertine in the Augustan, though occasionally a whole section was in concrete. A comparison with the brief reports given of the northern and southern basins makes the inference strong that they also belong mainly to the Augustan epoch even though advantage was taken of earlier drains wherever feasible. A complete study of the sewers would undoubtedly reveal plenty of instances of later repairs.