Rome commences at a point--Piazza del Popolo--and spreads out
southwards like a fan, the western extremity being occupied by the
Vatican, and the eastern by the Lateran; both these head-quarters of
the Papacy are isolated from the rest of the city. Modern Rome
occupies the valley of the Campus Martius, which was outside ancient
Rome, and the hills that abut it. Rome is divided into two unequal
parts by the river Tiber, which enters the line of the walls, with the
Popolo on its left. For a short distance it flows southwards; then it
makes a great bend to the west; then again takes a southerly
direction; and at the island again turns westerly. One mile south of
the Popolo Gate is the Capitoline Hill, the Arx of ancient Rome,
dividing, as it were, Old from New Rome. It rises two hundred yards
east of the Tiber, and from it in an eastern direction lie the other
six hills, curving in a horse-shoe form round the Palatine till the
Aventine abuts the river. Of the hills, the Palatine, Capitoline,
Cœlian, and Aventine were only isolated mounts, the Quirinal,
Viminal, and Esquiline being three spurs jutting out from the high
tableland on the east side of Rome. These hills can easily be
distinguished from the Tower of the Capitol; but the best way to
understand them is to walk round them. Then it will be seen that they
are hills indeed; and if we take into consideration that the valleys
have been filled in from thirty to forty feet, and that the tops of
the hills have been cut down, we may get some idea of their original
height. Rome still occupies four of them; but the Aventine, Cœlian,
and Palatine are left to ruins, gardens, and monks.
The original Rome was on the Palatine, and as the other hills were
added they were fortified; but it was not till the time of Servius
Tullius that the seven were united by one system of fortifications
into one city. The plan was simple. From the Tiber a wall went to the
Capitoline, and from that to the Quirinal; across the necks of the
three tongues the great agger was built, then across the valleys from
hill to hill till the wall again reached the river under the Aventine.
The aggers across the valleys were built right up towards the city, so
that the hills on either side protected the walls and gates commanding
the approach. Of all the maps of Rome that have been published, the
new one accompanying this work is the only one which correctly shows
the line of the Servian fortifications.