coast of Central Italy must have become increasingly shallow. This
result may not improbably have been expedited by that uplift of the
whole region to which reference has above been made. In course of
time, not only would volcanic cones appear as islands above sea-level,
but the action of winds, waves and tidal currents would throw up
bars or _lidi_, like those of Venice or those of more ancient date
which traverse the alluvial plain on either side of the mouth of the
Tiber. Further deposition of sediment, either from the volcanoes or
from the torrents of the Apennines, would lead to the silting up of
the lagoons between these bars. The hollows on the newly gained land
would eventually become fresh-water lakes, and the drainage from
the mountains would find its way by numerous channels across the low
plain into the sea. Thus, the Tiber, escaping from its narrow estuary
among the hills not improbably continued its southwesterly course, so
as to pass across what afterwards became the great volcanic district
of Bolsena and to enter the sea somewhere between Civita Vecchia and
Orbetello. The Anio would thus at that time be the main stream in the
Roman Campagna.
From the layers of lacustrine or fluviatile deposits in the tuff and
also from cavities and fissures in the limestone-hills, which then as
now rose abruptly from the edge of the volcanic plain, an interesting
series of organic remains has been obtained which throw a vivid light
upon the plants and animals of the centre of Italy in the volcanic
period. So far as yet discovered, the flora was on the whole similar
to that which still survives in the district. But the fauna was
strangely different. If the remains have been correctly identified, the
land animals of the time consisted of a curiously mixed assemblage,
including, on the one hand, many forms which have long been extinct,
together with some which still inhabit the surrounding region; and on
the other hand, quadrupeds characteristic of southern Europe or Africa,
as well as a few whose descendants are only found much farther north.
The open glades were traversed by various species of deer, gazelle and
wild ox, most of which are no longer living but which comprised the red
deer and the reindeer. There were likewise herds of more than one kind
of horse, whose bones have been found at some places in great numbers.
The caverns and clefts in the hills were tenanted by lions and hyenas,
lynxes and wild cats. The woods were haunted by brown bears, badgers,
wolves and foxes. Strangest of all the denizens of the region were the
huge pachyderms--mastodons, elephants, and rhinoceroses, including that
northern form, the mammoth. Beavers built their dams across the smaller
streams, while the hippopotamus disported himself in the rivers, which
were likewise tenanted by several species of aquatic tortoises. There
is occasionally something strangely incongruous in the circumstances
under which the remains of these primeval creatures are found in
places that have long been known only from their association with the
course of Roman history. One of the most singular examples of this
contrast was seen in the recent unearthing of a well-preserved tusk of
a hippopotamus a few inches underneath the pavement of the atrium of
the Vestal Virgins in the Forum Romanum. There can be little doubt that
the main part of this curiously varied fauna had established itself in
Italy long before the volcanoes first began their eruptions and that
many of its most singular and characteristic members continued to live
on during the volcanic period, for their remains have been exhumed from
some of the later deposits. A few like the otter, the mole, the hare
and the fox have remained in this region down to the present day.
It was after the Campagna had become a land-surface, tenanted by this
remarkable assemblage of animals, that the manifestations of volcanic
energy reached their climax. Instead of finding outlets in many minor
vents that discharged showers of ashes and stones, it now broke out
in a few large orifices from which not only copious discharges of
fragmentary materials, but also streams of lava were emitted. In
the district around Rome this greater localisation and more violent
activity were specially concentrated in two areas separated from each
other by an intervening plain about thirty-five miles broad. On the
south side of this plain, the group of the Alban Hills was built up
by many successive eruptions; on the north side, a chain of important
vents stretched from Bracciano northwards to the great crater of
Bolsena. Of these two areas, the southern comes more closely into
connection with Rome and the Campagna, and as it tells its story
vividly and fully, it claims our more special attention.
The Alban Hills, so striking a feature in the scenery of the region and
so indissolubly associated with the early chronicles of the Eternal
City, consist essentially of one great volcanic cone of the type of
Vesuvius, with a base about twelve miles in diameter. This cone has
been so greatly truncated that its summit, from one side of the rim
to the other, measures about six miles. The highest point of the rim
is 3,071 feet above sea-level. Inside lies the huge cauldron-like
depression that formed the original crater of the volcano, encircled
with steep slopes and rocky walls save on the north-west side towards
Rome, where the continuity of the crater-ring has been destroyed.
The abrupt truncation of this cone, the disappearance of the western
portion of its rim, the great size of its crater compared with the
total height of the mountain, and the existence of a later cone and
crater inside, together with a number of craters outside, suggest that
the energy of the volcano culminated in a gigantic explosion, whereby
the upper half of the cone, perhaps twice as high then as it is now,
was blown away, leaving inside a yawning chasm or caldera that opened
towards the west, where the wall was broken down. Such a paroxysm is
known to have occurred in the history of other volcanoes. In the case
of Vesuvius, for example, Monte Somma remains as a fragment of the
earlier and ampler condition of the mountain, before the catastrophe in
which the upper part and the southern half of the cone were blown away.
Since that event a new and smaller cone, forming the present Vesuvius,
has been piled up on the southern segment of the old crater-rim.
The explosion that eviscerated the Alban volcano must have caused
widespread desolation over the surrounding country. It was not
improbably followed by a long interval of repose. But the subterranean
energy was not exhausted, though it never again showed itself on so
vigorous a scale. We can trace, indeed, the signs of its gradual
enfeeblement. When it recommenced its activity the vent, which served
as the channel by which its eruptions took place, still retained its
central position. Round this vent a new but much smaller cone, bearing
witness to less vigour of eruption, was built up in the middle of the
crater. This younger mass rises in Monte Cavo to a height of 3150 feet,
the highest elevation on the whole mountain. It encloses a well-marked
crater with the flat plain of the Campo di Annibale at its bottom.
Eventually the central orifice came to be choked up by the lava that
had risen and solidified with it, and as the volcanic forces still
sought an outlet to the surface, they were compelled to find egress at
other and weaker points of the volcano. At least two explosions took
place on the old crater-rim and produced the deep-sunk and singularly
impressive lakes of Albano and Nemi. Others broke out on the flanks
of the great cone. Of these, the largest is marked by the crater of
the Valle Arriccia, but at least two dozen of smaller size have been
discriminated by the geologists of the Government Survey round the
outer slopes of the volcano. These lateral vents not improbably mark
the sites of the last eruptions.
While the Alban Mount was heaped up on the southern margin of the
Campagna, another independent series of volcanoes rose on the northern
border. The Lago di Bracciano marks the position of the vent that lay
nearest to Rome. The huge cavity in which this sheet of water lies
is some six miles in diameter and not improbably owes its origin to
another and still more stupendous explosion than that of the Alban
Hills. The level of the lake is 538 English feet above the surface of
the Mediterranean, and as the water is as much as 900 feet deep, the
bottom is 362 feet below sea-level. The crater wall still rises in
the Rocca Romana to a height of 1,437 feet above the sea, or 900 feet
higher than the lake which it encloses. Numerous streams of lava have
poured down the outer slopes of the cone, especially on the southern
flank. A few minor craters have been opened on its east side, and all
round there still rise warm springs and emanations of sulphuretted
hydrogen. To the north of this great vent lies another of similar
character and origin but of smaller size, which now contains the Lago
di Vico. The surface of this lake, which stands at a height of 1,663
feet above sea-level, is encircled by a crater-wall which on the west
side mounts to nearly 1,600 feet above the sheet of water which it
encircles. To the northeast rises the volcanic mass of Monte Cimino,
3,464 feet high. Still farther north is the largest of all the Italian
crater-lakes, the Lago di Bolsena, which is no less than twenty-eight
miles in circumference.
Having regard to the great variety of material in these different
volcanic piles and to the evidence furnished by them that they were
formed by many successive eruptions, perhaps separated from each
other by long intervals of time, we cannot but be impressed with the
antiquity of the great subaërial cones and the protracted period
required by each of them for its formation. We must remember, too,
that from the very beginning of their history they were ceaselessly
attacked by the various agents of subaërial erosion. The first showers
of rain that fell on their young slopes of incoherent ashes gathered
into runnels which would plough furrows in their descent to the plain.
Century after century these watercourses were cut deeper and wider
until they have attained the dimensions of the numerous _fossi_ that
now radiate from each crater-rim. In some cases these lines of erosion
served as channels for the streams of lava that were poured down the
slopes, as may be well seen on the southern flanks of the Bracciano
volcano.
In most instances the molten rock stopped short on the flanks of its
parent mountain, but it occasionally descended into the plain, as in
the familiar example on the Via Appia, where the stream flowed from the
side of the Alban volcano for some six miles to within a short distance
of the site of the future capital of the world. The lava is here a
firm, compact, durable stone admirably adapted for pavements, a use to
which it has been extensively put for more than two thousand years,
both within the walls and on the great high roads that radiate from
them. Here, again, we see how bountifully Rome was favoured in regard
to the materials needed for the construction of a great city.
The heaping of so much volcanic rock over the surface of the country
must have greatly modified its topographical features. The drainage
would especially be affected. Streams descending from the Apennines
would find their direct passage to the sea blocked by the newly
formed ridges, hills and mountains, and they might have to make long
circuits before finding an exit. Lakes would gather in the hollows of
the irregularly deposited tuff and others would fill up the cavities
blown out by explosions, so as to become crater-lakes. The case of the
Tiber may be cited in illustration of the deflection of drainage. In
earlier times, as I have already remarked, this river probably flowed
southwestwards across the site of the volcanic district of Bolsena and
Viterbo; but in consequence of the subsequent eruptions, the lower
part of its course was buried and the stream, diverted at a right
angle, was made to run southeastwards, skirting the volcanic heights
until, near Monte Soracte, it reached the plain between the base of the
Bracciano and that of the Alban volcano, where it was able at length to
find a seaward passage across the site of the future Rome.
That the early races of man witnessed and suffered from the latest
eruptions may well be believed. The oldest traces of human occupation
are stone implements, found more particularly in the higher
river-gravels which, though they must undoubtedly date back to a
remote antiquity, are certainly much later than the general mass of
the tuff of the Campagna. Traditions of volcanic events seem to have
survived into historic times. The pages of Livy, for example, contain
references to showers of stones that fell in various places during
the early centuries of Rome, and were regarded as portents of divine
interposition in human affairs. We are told that in the hundredth year
of the city showers of that kind fell on the Alban Mount, accompanied
with loud noises from the wood on the summit. Again, in the year 540,
fearful storms are said to have been experienced, while a fall of
stones on the Alban Mount went on continuously for two days. Nineteen
years later, amidst a miscellaneous series of prodigies, it is said
to have rained stones at Aricia, Lanuvium, and on the Aventine. Such
references have by some writers been interpreted as proofs of true
volcanic eruptions, thus bringing the activity of the volcanoes around
Rome well down into historic time. A supposed confirmation of this
conclusion has been claimed to have been found on the ridge of Castel
Gandolfo, where numerous burial urns containing cremated human remains
have been unearthed five or six feet below the surface of the ground.
Associated with some of these interments were fibulæ and objects in
amber and bronze, together with specimens of Etruscan or Italo-Greek
pottery of a beautifully Archaic pattern. It has been maintained that
the superficial covering of volcanic material (which has even been
called 'lava') has been the product of one or more volcanic eruptions,
subsequent to the time of the burials, and hence that these eruptions
must have taken place not only after the Stone Age, but even so late
as after the coming of the Greek colonists. It has even been held that
the shepherds of the Alban Hills, driven away from these heights by
the violence of the volcanic disturbances, took refuge on the Seven
Hills, where they founded the city and empire of Rome. More probably
the volcanic detritus which overlies the cinery urns is of much more
ancient date, the interments having been made by digging down through
it, long after the last eruptions of the volcano had ceased.
It is not necessary, however, to refuse credence to all the portents
recounted by Livy. More than two thousand years ago, when the events
cited by him are alleged to have happened, the volcanic forces of
the region must have been more potent than they now are, and various
manifestations by them may have occurred which we do not expect to
see repeated at the present day. Though the subterranean fires have
been steadily dwindling, they even yet retain heat enough to supply
many thermal springs and to discharge large quantities of sulphuretted
hydrogen gas. Now and then, also, they show a sudden though local
manifestation of energy, and cause disturbances sufficiently alarming
to fill the population with superstitious dread. An instance of this
kind, which was witnessed within living memory, may here be cited as
affording a reasonable explanation of some of the supposed supernatural
prodigies recorded in Roman history. On the south side of Monte Soracte
lies a dried-up lake which, no doubt on account of its offensive
sulphurous exhalations, was called the Lagopuzzo, or Stinking Mere. The
late Professor Ponzi has recorded that towards the end of the month of
October, in the year 1831, a series of cracks suddenly opened on this
old lake-bottom and a large piece of flat ground lying between them
gradually sank out of sight. At the same time subterranean rumblings
commenced and grew in intensity, mingled with detonations like the
thundering of cannon. The surrounding population fled in terror to the
neighbouring hills, whence looking back, they could see earth and water
thrown up from the fissures, while a thick coating of dust fell over
the whole district. The eruption began towards sunset and reached its
culmination about seven o'clock in the evening. Next morning it was
found that the Lagopuzzo was traversed by a chasm with vertical walls,
at the bottom of which lay a sheet of water covered with a white scum
and giving off a powerful odour of sulphuretted hydrogen. The ground
around the cavity was strewn with pools of water and lumps of erupted
earth, sometimes seventy cubic feet in size, which had been ejected to
a distance of one hundred feet. The cannon-like detonations continued,
but grew gradually less violent, each of them being accompanied by a
copious discharge of the ill-smelling gas which threw the water into
such commotion as to undermine the surrounding walls of alluvial earth
and to cause portions of them to fall into the abyss. After a few days
the disturbances ceased, leaving as their memorial a cross-shaped chasm
upwards of three hundred feet in diameter, with walls rising some
fifteen feet above the water, which was ascertained to be about one
hundred feet deep.
Many such incidents as this may have been experienced in the history
of ancient Rome. They would be quite enough to fill the minds of the
populace with terror, and to call for a nine days' expiation and
lustration of the city. The traditional legend of the chasm that opened
in the Forum, and into which Curtius threw himself in full armour to
propitiate the gods and save the city, may very well have been founded
on a real event of this nature. The lake or quagmire in the Forum may
have been another Lagopuzzo, rent open by an outburst of gas. The
subterranean rumblings and bellowings (_boati_), which were accounted
such dire portents in old times, were exactly repeated near Monte
Soracte in the autumn of 1831.
Before we pass from this volcanic period to the consideration of the
next phase in the history of the Campagna, it may be noted, as an
interesting feature in the growth of the Italian peninsula, that the
subterranean energy has been slowly dying out from north to south. The
volcanoes of Central Italy have long since entered into the closing or
Solfatara stage, when only steam, hot vapours, and gases are emitted.
But at the southern end of the chain lies the still vigorous Solfatara
of Naples, with the various cones around it, some of which have been
in eruption within the last few centuries, while Vesuvius continues to
maintain a persistent though variable activity. Still farther south
lie the Æolian Islands, where Volcano occasionally breaks out, while
Stromboli remains, as it has done since the beginning of authentic
history, in a state of constant ebullition and eructation. At the far
extremity of the volcanic belt rises the colossal cone of Etna, which
from time to time displays an energy worthy of its place among the
great volcanoes of the globe.
III. We have traced how the platform of the Campagna has been step by
step built up, partly by the accumulation of silt, sand, and gravel
on the sea-floor, partly by submarine volcanic ejections, and partly
by a widespread uplift of the whole region above sea-level, and by
continued subaërial volcanic activity. We now reach the third and last
section of our history in which we have to consider how the present
topography of the ground has been produced. A little reflection will
convince us that, even before its elevation into land, the submerged
surface of the district was probably far from presenting a dead flat,
though it no doubt approached nearer to that form than it has ever
done since. In spite of the levelling action of waves and currents,
the sea-floor in front of the Apennine chain must have abounded in
inequalities caused not only by the scour of the water, but more
especially by the irregular distribution of the volcanic débris and
the greater accumulation of the material around the submarine vents.
Such inequalities would not only remain but grow more pronounced when
the sea-bottom became a land-surface. Every subsequent outbreak of
eruptive energy would aggravate them. But ultimately more potent still,
because incessant in its operation, would be the influence of the
various subaërial agencies by which the land is continually abraded.
It is to these agencies that we must mainly ascribe the present
topography of the district. By a ceaseless process of sculpture, the
volcanic platform has been ultimately carved into hillock and ridge,
crag and cliff, valley and ravine. The tools which Nature has employed
in this task have been the air, with its wide range of temperature and
moisture, frost, rain and running water in all its manifold forms, from
the tiniest rill to the broad current of the Tiber.
The key to the interpretation of the origin of the scenery of the
Campagna is supplied to us by the lines of drainage. On the uplift
of the region into land, the streams that descended from the steep
front of the mountains would make their way seaward along the lowest
levels which they could reach. The channels thus chosen by them would
be maintained for the future, save where some landslip or volcanic
eruption drove them to seek new courses for their waters. Failing
such exceptional causes of diversion, the original lines of drainage
would gradually be carved deeper into the framework of the land by the
erosion of the water running in them. Thus the streams and the valleys
which they have cut out for themselves are the most ancient features
of the topography. Between them lie ridges and plateaux, which have
gradually become prominent owing to the excavation of the intervening
hollows. These eminences, though not subject to such marked and rapid
demolition as the channels where running water is allowed free play,
nevertheless undergo an appreciable decay. Attacked by the alternate
expansion and contraction, due to the heat of clear Italian noons,
quickly followed by the chill of starry Italian nights, the faces
of the crags and cliffs are slowly disintegrated. Heavy rain washes
off the loose crust and exposes a fresh surface to renewed attack.
Alternate saturation by rain and drying in sunshine, the effects of
frost and the abrading influence of wind, all contribute their share to
the process of carving. By this universal process of denudation, while
the topographical features have been made continually more pronounced,
a considerable thickness of rock has no doubt been removed from the
general surface of the whole ground since its elevation into land.