populace, who formed one vast penitential procession, and saw the avenging angel alight on the mausoleum of Adrian and sheath his sword in sign that the plague was stayed; or to that terrible day when the ferocious mercenaries of the Constable de Bourbon and the wretched inhabitants given over to sack and slaughter swarmed across together, butchering and butchered, while the troops in the castle hurled down what was left of its classic statues upon the heads of friend and foe, and the Tiber was turned to blood! [Illustration: THE CASTLE OF ST. ANGELO.] [Illustration: ISLAND OF THE TIBER.] From the bridge of St. Angelo the river is lost again for a long distance, although one can make one's way to it at various points--where at low water the submerged piers of the Pons Triumphalis are to be seen, where the Ponte Sisto leads to the foot of the Janiculum Hill, and on the opposite bank the orange-groves of the Farnesina palace hang their golden fruit and dusky foliage over the long garden-wall upon the river--until we come to the Ponte Quatro Capi (Bridge of the Four Heads) and the island of the Tiber. This is said to have been formed in the kingly period by the accumulation of a harvest cast into the stream a little way above, which the current could not sweep away: it made a nucleus for alluvial deposit, and the island gradually arose. Several hundred years afterward it was built into the form of a ship, as bridges and wharves are built, with a temple in the midst, and a tall obelisk set up in guise of its mast. In mediæval days a church replaced the heathen fane, and now it stands between its two bridges, a huddle of houses, terraces and gardens, whence one looks down on the fine mass of the Ponte Rotto (Broken Bridge), whose shattered arches pause in mid-stream, and across to the low arch of the Cloaca Maxima and the exquisite little circular temple of Vesta. From here down, the river is in full view from either side until it passes beyond the walls near the Monte Testaccio--on one side the Ripa Grande (Great Bank or Wharf), a long series of quays, on the other the Marmorata or marble landing, where the ships from the quarries unload. Here, on each side, all sorts of small craft lie moored, not betokening a very extensive commerce from their size and shape, but quaint and oddly rigged, making a very good fore-or back-ground, according as one looks at the picture. The Marmorata is at the foot of the Aventine, the most lonely and unvisited of the Seven Hills. From among the vegetable-gardens and cypress-groves which clothe its long flank rise large, formless piles, whose foundations are as old as the Eternal City, and whose superstructures are the wreck of temples of the kingly and republican periods, and palaces and villas of imperial times, and haughty feudal abodes, only to be distinguished from one another by the antiquary amid their indiscriminate ruin and the tangle of wild-briers and fern, ivy and trailers with which they are overgrown.