Several causes led to the abandonment of the _agro romano_. The neglect of the roads and the ruin of the aqueducts, which cut off the water supply, the poverty of the despoiled landlords, and the general insecurity following the incursions of the barbarians in the fifth and sixth centuries, brought about a rapid depopulation and gradually turned the _agro_ into a pest-bound desert. It would seem that malarial fever is virtually indigenous to the soil of the _agro_, besetting every region as soon as man deserts it. It did not make its appearance, we may suppose, in the inhabited towns of the classical period, but that it existed before the middle ages, the popular date for its appearance, is shown by the allusions of classical writers since the time of Augustus and by the existence of several temples to the goddess Fever. In Rome itself it is the persistent belief, which appears to be abundantly confirmed by statistics, that the more building is extended and the horribly noisy paved streets are multiplied, the faster the evil diminishes; for the malarial miasma is held to be an exhalation of the soil, and where earth is freshly turned there is danger. As we all know, it has been quite recently shown that the microbe of malaria is carried by mosquitoes, mosquitoes abound where water abounds, and one of the reasons for the unhealthiness of the _agro_, one of the greatest obstacles to its reclamation, is that there are not less than ten thousand little water-courses which filter down to the valleys, creating marsh and stagnant pools. The evil may really date from the last years of the republic, which saw the displacement of the small freeholders by the large landowners, of the old free labour by slave labour, and the consequent fatal depopulation of the _agro_. But during the middle ages, from the sixth century onwards, all the causes were intensified, and the difficulties which now beset the secular problem of the restoration of agriculture in the Roman campagna and the expulsion of malaria, resolve themselves "into a vicious circle"; for men cannot live there until the malaria is exorcised, and until men live there the malaria will remain in possession. No less than seventy-nine measures for what is known in Italy as the _bonifica dell' agro romano_ have from time to time been projected; and whether Italy will succeed where the popes failed is still doubtful. The initial necessity, the drainage of the campagna, seems in itself to be a task too great for Hercules. For the last four years the military _Croce Rossa_ has perambulated the campagna during the summer and autumn months, combating the malaria with doctors and medicines. It is hoped that this will be followed by the establishment of a larger number of permanent sanitary stations. Since 1870 millions of eucalyptus trees have been planted as air purifiers especially at the little railway stations and other inhabited sites. It is not forgotten that the