These seem to have been commenced by Tarquinius Priscus, and completed
by Servius Tullius, and so called by his name.
"He [Tarquinius Priscus] was the first who built the walls of the city
[of which the structure was extemporary and mean] with stones,
regularly squared, each being a ton weight" (Dionysius, iii. 68).
Tarquinius (616 B.C.) "intended also to have surrounded the city with
a stone wall, but a war with the Sabines interrupted his designs"
(Livy, i. 36).
"He set about surrounding with a wall of stone those parts of the city
which he had not already fortified, which work had been interrupted at
the beginning by a war with the Sabines" (Livy, i. 38).
"He [Servius] surrounded the city with a rampart, trenches, and a
wall, and thus extended the Pomœrium," 578 B.C. (Livy, i. 44).
"As the Esquiline and Viminal Hills were both of easy access from
without, a deep trench was dug outside them, and the earth thrown up
on the inside, thus forming a terrace of six stadia in length along
the inner side of the trench. This terrace Servius faced with a wall,
flanked with towers, extending from the Colline to the Esquiline gate.
Midway along the terrace is a third gate, named after the Viminal
Hill" (Strabo, v. 3).
"Tullius had surrounded the seven hills with one wall" (Dionysius, iv.
14).
The seven hills were not surrounded, strictly speaking. Each hill
formed a bastion, and aggers, or curtains of earth faced with stone,
were built across the valleys, uniting these bastions. The Esquiline,
Viminal, and Quirinal, being ridges jutting out of the table-land and
not isolated hills, had one long agger built across their necks.
"Some parts of these walls, standing on hills, and being fortified by
nature itself with steep rocks, required but few men to defend them,
and others were defended by the Tiber.... The weakest part of the city
is from the gate called Esquilina to that named Collina, which
interval is rendered strong by art; for there is a ditch sunk before
it, one hundred feet in breadth where it is narrowest, and thirty in
depth. On the edge of this ditch stands a wall, supported on the
inside with so high and broad a rampart that it can neither be shaken
by battering-rams nor thrown down by undermining the foundations. This
rampart is about seven stadia in length and fifty feet in breadth"
(Dionysius, ix. 68).
This grand agger can be traced almost in its entire extent, as also
the smaller aggers. There seems to have been no wall--that is, stone
or earth fortification--between the Aventine and Capitoline, the Tiber
being considered a sufficient defence.
"The city, having no walls in that part next the river, was very near
being taken by storm" (Dionysius, v. 23) when Lars Porsena advanced to
attack the city, after having taken the Janiculum, intending to cross
the river by the only bridge, which, as we know, was defended by
Horatius Cocles, and broken down by the Romans in his rear.
The walls of Servius Tullius were strengthened at the time of the war
with Gabii.
"Tarquinius Superbus was particularly active in taking these
precautions, and employed a great number of workmen in strengthening
those parts of the city walls that lay next to the town of Gabii, by
widening the ditch, raising the walls, and increasing the number of
the towers" (Dionysius, iv. 54).
"On the eastern side it is bounded by the Agger of Tarquinius
Superbus, a work of surpassing grandeur; for he raised it so high as
to be on a level with the walls on the side on which the city lay most
exposed to attack from the neighbouring plains. On all the other sides
it has been fortified either with lofty walls or steep or precipitous
hills; but so it is that its buildings, increasing and extending
beyond all bounds, have now united many other cities to it" (Pliny,
iii. 9).
"After Camillus had driven out the Gauls, both the walls of the city
and the streets were rebuilt within a year" (Plutarch, "Cam." 32).
"The legions being brought to Rome, the remainder of the year was
spent in repairing the walls and the towers," 350 B.C. (Livy, vii.
20).
"They received a charge from the senate to strengthen the walls and
towers of the city," 217 B.C. (Livy, xxii. 8).
After the republic was firmly established, and the boundaries of the
state enlarged, the walls of the city became obsolete, and it was to
all intents and purposes an open city until the time of Aurelian.
"All the inhabited parts around it [the city], which are many and
large, are open, and without walls, and very much exposed to the
invasion of an enemy. And whoever considers these buildings, and
desires to examine the extent of Rome, will necessarily be misled, for
want of a certain boundary that might distinguish the spot to which
the city extends, and where it ends. So connected are the buildings
within the walls to those without, that they appear to a spectator
like a city of an immense extent" (Dionysius, iv. 13).