The latter fountain looks as if it were the older, for, as it is situated in the southeast corner of the wide piazza, it is exposed to the full sweep of the Tramontana, or north wind, which has fretted and worn in no small degree the surface of the travertine. It may have been the more sheltered position of the northeast corner which determined the location of Paul V’s fountain, the earlier of the two. In the spring the Altieri fountain is the more beautiful because at that time that portion of the Colonnade which forms its background reveals vistas of foliage, while the moss web woven about the crown of the shaft is of a more brilliant green and the lower basin is full of the same aquatic growth swaying with the motion of the water. The Acqua Paola, which feeds these fountains, comes, in the last instance, from the summit of the Janiculum, and therefore their central jets are flung upward to a height of sixty-four feet, far above the balustrade crowning Bernini’s lofty colonnades, which form the background of the piazza. This height exceeds by from twenty-four to thirty-four feet the height of the English and French fountains; and whereas in the fountains of London and Paris the supply and force of the water varies with the season of the year and the time of day (the Trafalgar Square fountains in summer play thirteen hours out of the twenty-four and in winter only seven), the abundance and power of the water in these great Roman fountains is unfailing and unchanging. At midnight, at high noon, in summer, in winter, they are always flowing, and the splash and wash of the water makes them akin to the cascades of Nature.