Now, whatever may be the secret of these passages, it scarcely admits of doubt that they were designed for an entrance to the grotto from the island. Capri is so thickly studded with Roman works of the emperors Augustus and Tiberius, and possesses so few others, that there is little risk in attributing the construction of this passage to Roman hands. But what did the Imperial courtiers see, if they did indeed come down those winding passages and stand on the rock shelf where the greedy boy now bargains loudly for francs? Was it the same blue wonder that we see? The answer is certain. The miracle of colour depends directly on the level of the water, and in Roman days the arch was far too high to permit the necessary refraction or colouration of the rays of sunlight. This is proved in two ways. Firstly, there is unanswerable evidence in the hands of geologists and naturalists that the level of the sea in Roman days was many feet lower than at present. Secondly, the fact that there was more of the archway to be uncovered has been proved by Colonel MackOwen, who explored it by diving, and who found not only that the original height of the entrance was six feet and a half, of which three feet are under water, but also that the base of the opening is formed by a flat, projecting sill, which appeared to have been set there by human hands. Moreover, this archway, which is now the sole entrance to the grotto, is but a poor substitute for a more ancient and incomparably larger doorway still existing, but now submerged, and measuring as much as fifty feet by forty feet, which must have let white sunlight into the cavern as long as it stood above the water. There is thus not much reason for supposing that Roman eyes ever beheld this wonder of the world. Whether seen or not seen by an occasional bold intruder, this unique marvel lay silent and unvisited through all the Middle Ages, accounted even by our grandfathers as a haunt of fiends and a centre of mysterious terrors. It is not easy now to catch a moment in which the cave is silent. Only early in the morning one may find its charm completely undisturbed, and carry away a recollection of unearthly mystery and beauty which will remain a precious possession throughout life. There is much in Capri that is unparalleled. If I have set the Blue Grotto first, that is not because more beauty is found there than exists elsewhere upon the island. It may be beauty of a rarer kind; I do not know. All Capri is a gem, and that which one sees from the island is lovelier still than anything upon its shores.