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. THE PLAN OF OUR RAMBLES. From the Piazza del Popolo four great lines of thoroughfare intersect the city, and passing up one of these for a few hundred yards we may count five lines. First we take the centre thoroughfare; then the two lines on its right; then the two upon its left: in this way, by dividing Rome up into five Rambles, pointing out as we go along every place of interest to the right and left, we mark out for a day's work no more than can be thoroughly done. Having thus seen the city, we take the environs outside each gate, commencing at the Porta del Popolo and working round by the east, with the exception of the Porta Appia, which leads out on to the Appian Way. As this Way presents so many points of interest, and as no visitor should think of leaving Rome without "doing it," we have made it a special Ramble for their benefit. HEALTH AND CLIMATE. Perhaps the health of no city in the world is so much talked about by people who know nothing whatever of the subject, as Rome. We meet with many visitors entertaining all sorts of curious ideas of the health of Rome--what they may and may not do; and when we ask them their authority they cannot give any, but "they have heard so." There seem to be mysterious ideas and impressions floating about that get lodged in some minds no one knows how. People get ill in Rome, of course, just as in any other place; but more than half the sickness is caused through their own imprudence, such as getting hot and going into cold places, and going "from early morn till dewy eve" without rest and refreshment. In all hot climates certain precautions should be observed, and then there is no fear. We ourselves have lived many years in this much-abused climate, never knowing any illness, and enjoying far better health than when residing in London. O ye rain, mud, and fog!