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 volcanic ejection, and partly by a widespread uplift of the whole region above sea-level, and 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 leveling 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 this 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 a clear Italian noon, quickly followed by the chill of a starry Italian night, 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.

While it is thus easy to realize, as one traverses the Campagna, how its main topographical characteristics have been evolved, there is a special fascination in pursuing the investigation of particular features and trying to trace their origin in detail. Take, for instance, the story of the valleys. I can hardly imagine a more delightful task for a lover of geology than to work out the history of the Tiber—an investigation which from the point of view we are here considering still remains to be accomplished. Even from any of the hills of Rome it is not difficult to follow some of the stages of this history. We have seen that the river may have flowed at first southwestward from its estuary among the Todi hills across the site of the volcanic district to the sea somewhere north of Civita Vecchia. We have further found that the volcanic eruptions which gave rise to the long line of heights between Aquapendente and Bracciano probably blocked up the older channel, and turned the stream towards the southeast and for many miles kept it from once more bending seawards until at last it found its escape across the low ground of the Campagna. Looking from the Monti Parioli up the broad strath, we see the Tiber meandering through its flat alluvial plain which, from a width of a mile and a half, suddenly contracts immediately below us to less than a third of that space. The meaning of this constriction will be understood if we remember the position of the sheet of hard travertine to which allusion has already been made. When the river began to flow across this tract of country, the general level of the ground, not yet reduced by prolonged denudation, was no doubt a good deal above what it is now, and the bed of the stream may even have lain at a higher level than the tops of the present ridges in which Rome is built. After traversing the volcanic plain the Tiber reached the western margin of this tract near where the Monti Parioli now rise. It then flowed southwards between the slopes of Monte Mario and the edge of the volcanic accumulations. It cut its way downward through the upper parts of the tuff, and at length encountered the sheet of travertine near the Ponte Molle. This hard stone would form for a time a barrier to the erosion which must have been comparatively rapid among the soft overlying tuffs. The river, ponded back into a lake-like expansion in front of the mouth of

the Anio, was made to sweep in a wide curve into the softer Pliocene strata of the Vatican ridge on the right bank. The travertine extends through the Parioli ridge and round the base of the Pincian Hill. A similar rock emerges in the precipitous bank on the west side of the Aventine, and farther south at the Monte Della Creta, opposite the Magliana bridge. Even where this resisting stone disappears, its place has often been taken by a variety of tuff much more compact than the usual rock of the district. It is the presence of these more durable kinds of stone that has curbed the erosive progress of the river on its left bank through the area on which the city stands. Where these barriers to its action were locally absent the river was able to scoop out bays and recesses among the softer parts of the tuffs. The Capitoline, Palatine, Aventine and Celian hills have survived as more or less isolated eminences from their fortunate possession of a more obdurate stone than the loose granular tuff of the surrounding Campagna. They once rose as islands out of the flood plain, and their steep sides, such as the Tarpeian rock and the cliffs that surrounded the original Roma Quadrata, owed their precipitousness mainly to the scour of the Tiber as it swept past their base.

Hardly less attractive would be the task of deciphering the history of the rough craggy ridges and broad, smooth plateaux which form such distinctive features in the scenery of the Campagna. In this investigation we would mark how these differences of contour have mainly arisen from variations in the character of the volcanic tuff. Where the rock has possessed little coherence and has consequently yielded more easily to the weather, it has crumbled away for the most part into gentle slopes which have been more or less shielded from further decay by a mantle of vegetation. But where the loose ashes and scoriæ have been accompanied with much fine dust and have consolidated into a hard, compact stone, this material has survived to form the more rugged features of the scenery. Every stage in the progress of the sculpture may be instructively seen at the edge of the volcanic plain, where it winds round the projecting spurs and curves into the retreating hollows and bays of the great Apennine wall. Little imagination is needed to picture this plain as a sea-floor over which the waves rolled along the base of the mountains. But when it was raised into land the torrents from the uplands began to dig out of it winding channels, which were gradually deepened into gullies that unite into wider ravines as they descend. Between those defiles portions of the old plain have been left, along the sides of which the successive sheets of tuff run as bold ribs or as green slopes, according to their relative durability. Here and there one of these outliers, girdled round with vertical walls of rock, rises as an almost inaccessible platform above the ravines around, and has served as the site of some pre

historic citadel or of some mediæval fortalice. All over the Campagna, indeed, from the very earliest ages, advantage has been taken of such defensible sites. They were selected as positions for the cities of Latium and Etruria, art often aiding to scarp their sides into steeper and more continuous crags than Nature had provided. They supplied convenient sites for the abundant suburbana or country villas and manors of ancient Rome, and they were used over and again in the stormy Middle Ages for the erection of fortified farms and refuge-towers.

A discussion of the history of the Campagna would probably be regarded as culpably incomplete without at least a reference to the causes that have led to the solitude and desolation of the region. There can be little doubt that in the days of the Empire the plain was thickly peopled and well cultivated. It could not have been the fever-stricken place which it has since become. The wealthy Romans were delighted to escape from the tumult of town to their quiet and healthy retreats in the country where, amid the pleasures and occupations of their farms, they could spend the hottest, and what is now the most insalubrious, season of the year. Yet there would seem to have been even then malarious tracts in the Campagna. Cicero boasts of the healthiness of Rome, compared with the pestilential character of the surrounding district. The porousness of the tuff all over the country, as I have above remarked, allows a large proportion of the rain to sink at once under ground, instead of flowing off into runnels and brooks. The water finds its way again to the surface at lower levels, either in the form of springs or oozing from the soil. In the hollows where the drainage accumulates, stagnant pools and marshes arise, which become the great nurseries of malaria. In the most flourishing days of Rome when the whole surface of the Campagna was populous and in full cultivation, attention was alive. to the importance of drainage. Probably most of the swampy tracts, whence mosquitoes now swarm, were then dry and turned over by the plough or the spade. The general processes of agriculture prevented the accumulation of stagnant water and rotting vegetation. But with the fall of Rome and the devastation of the Campagna by successive hordes of barbarians, the villas fell into ruins, the inhabitants were in great measure extirpated, the farms remained untilled, the soil was left untouched, the water was allowed once more to gather and the vegetation to decay in the hollows. In the well-known words of Gibbon, "The Campagna of Rome was speedily reduced to the state of a dreary wilderness in which the land is barren, the waters are impure and the air is infectious." Fever, which probably always found a home in various parts of the district, now stalked everywhere, until at the end of the twelfth century, when the population of the city had fallen to no more than 35,000 souls, Pope Innocent III. could de

clare that it was difficult to find there a man of forty years of age and hardly possible to meet with one of sixty.

No one will dispute that the sole, or at least the chief, cause of this longcontinued depopulation is to be found in the prevalence of malarious fever. Nor since modern science has so clearly revealed the nature and source of this decimating malady can there be any hesitation as to the more important steps that must be taken to restore the region to healthfulness and fertility. Schemes are now in contemplation to reclaim these wastes to cultivation and to repeople them with an industrious peasantry. While every lover of Italy will rejoice over the successful accomplishment of such a beneficent reform, those who have known the Campagna in the days of its desolation and have found in its weird loneliness and quiet beauty, in its monuments and memories of the past, an inexpressible delight, will perhaps be pardoned if they regretfully look back upon another of the charms of Rome which shall then have passed away.