e might be placed in ideal ramparts, the
experience of the past, and the dread of the future, induced the Romans
to construct fortifications of a grosser and more substantial kind. The
seven hills of Rome had been surrounded, by the successors of Romulus,
with an ancient wall of more than thirteen miles. [40] The vast enclosure
may seem disproportioned to the strength and numbers of the infant
state. But it was necessary to secure an ample extent of pasture and
arable land, against the frequent and sudden incursions of the tribes
of Latium, the perpetual enemies of the republic. With the progress
of Roman greatness, the city and its inhabitants gradually increased,
filled up the vacant space, pierced through the useless walls, covered
the field of Mars, and, on every side, followed the public highways in
long and beautiful suburbs. [41] The extent of the new walls, erected by
Aurelian, and finished in the reign of Probus, was magnified by popular
estimation to near fifty, [42] but is reduced by accurate measurement to
about twenty-one miles. [43] It was a great but a melancholy labor, since
the defence of the capital betrayed the decline of the monarchy. The
Romans of a more prosperous age, who trusted to the arms of the legions
the safety of the frontier camps, [44] were very far from entertaining
a suspicion, that it would ever become necessary to fortify the seat of
empire against the inroads of the barbarians. [45]

[Footnote 40: Plin. Hist. Natur. iii. 5. To confirm our idea, we may
observe, that for a long time Mount Caelius was a grove of oaks, and
Mount Viminal was overrun with osiers; that, in the fourth century, the
Aventine was a vacant and solitary retirement; that, till the time of
Augustus, the Esquiline was an unwholesome burying-ground; and that
the numerous inequalities, remarked by the ancients in the Quirinal,
sufficiently prove that it was not covered with buildings. Of the seven
hills, the Capitoline and Palatine only, with the adjacent valleys, were
the primitive habitations of the Roman people. But this subject would
require a dissertation.]

[Footnote 41: Exspatiantia tecta multas addidere urbes, is the
expression of Pliny.]

[Footnote 42: Hist. August. p. 222. Both Lipsius and Isaac Vossius have
eagerly embraced this measure.]

[Footnote 43: See Nardini, Roman Antica, l. i. c. 8. * Note: But compare
Gibbon, ch. xli. note 77.--M.]

[Footnote 44: Tacit. Hist. iv. 23.]

[Footnote 45: For Aur