Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
The tunnel which drains the Alban lake(18) presents the greatest resemblance to that of lake Copais. What are called Cyclopean ring-walls frequently occur in Italy, especially in Etruria, Umbria, Latium, and Sabina, and decidedly belong in point of design to the most ancient buildings of Italy, although the greater portion of those now extant were probably not executed till a much later age, several of them certainly not till the seventh century of the city. They are, just like those of Greece, sometimes quite roughly formed of large unwrought blocks of rock with smaller stones inserted between them, sometimes disposed in square horizontal courses,(19) sometimes composed of polygonal dressed blocks fitting into each other.
18. Cf. I. III. Alba
19. Of this character were the Servian walls. They consisted partly of a strengthening of the hill-slopes by facing them with lining-walls as much as 4 metres thick, partly--in the intervals, above all on the Viminal and Quirinal, where from the Esquiline to the Colline gate there was an absence of natural defence--of an earthen mound, which was finished off on the outside by a similar lining-wall. On these lining-walls rested the breastwork. A trench, according to trustworthy statements of the ancients 30 feet deep and 100 feet broad, stretched along in front of the wall, for which the earth was taken from this same trench.
--The breastwork has nowhere been preserved; of the lining-walls extensive remains have recently been brought to light. The blocks of tufo composing them are hewn in longish rectangles, on an average of 60 centimetres (= 2 Roman feet) in height and breadth, while the length varies from 70 centimetres to 3 metres, and they are, without application of mortar, laid together in several rows, alternately with the long and with the narrow side outermost.
The portion of the Servian wall near the Viminal gate, discovered in the year 1862 at the Villa Negroni, rests on a foundation of huge blocks of tufo of 3 to 4 metres in height and breadth, on which was then raised the outer wall from blocks of the same material and of the same size as those elsewhere employed in the wall. The earthen rampart piled up behind appears to have had on the upper surface a breadth extending about 13 metres or fully 40 Roman feet, and the whole wall-defence, including the outer wall of freestone, to have had a breadth of as much as 15 metres or 50 Roman feet. The portions formed of peperino blocks, which are bound with iron clamps, have only been added in connection with subsequent labours of repair.
--Essentially similar to the Servian walls are those discovered in the Vigna Nussiner, on the slope of the Palatine towards the side of the Capitol, and at other points of the Palatine, which have been declared by Jordan (Topographic, ii. 173), probably with reason, to be remnants of the citadel-wall of the Palatine Rome,
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Reference address : https://www.ellopos.net/elpenor/rome/1-15-art.asp?pg=32