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.