Tiberius nodded, and, Martialis turning round, saw, to his astonishment a narrow opening in the cell wall opposite to the door, and beside it Zeno standing smiling, with a lantern in his hand, ready to conduct him. ‘It leads to the grotto beneath, and so avoids busy eyes above,’ said the Emperor. ‘_Vale._’ The steward went through the secret opening, and Martialis followed down a narrow subterranean way for a considerable distance. The descent was continuous, and in some places by means of broad shallow steps. A door closed the exit, and when Zeno opened it he gave the key to his companion. ‘You must return to Capreae by no other way than this. On the upper door you will find a small knob on the left hand side; press it and you will be able to enter your cell again.’ Then desiring him to stand still lest he should fall into the water, the steward lit a torch, with which he had provided himself, and Martialis perceived they were in the largest of those wonderful caverns or grottoes which exist in various places in the island, along the foot of the sea‐ washed cliffs. As one of the wonders of the island he had been in it before, though, of course, entering from the sea; and had seen with delight and wonder the dazzling effects of the blue refraction of the light in daytime, and the lovely silvery colour which the deep water lent to every object immersed therein. The torch of Zeno gave sufficient light by which to unmoor a light skiff which floated beside the little landing‐ place on which they stood. The red glare fell on the still, dark, deep water, but failed to pierce to the lofty roof, or yet to the full circuit of the cavern, which nature had curiously domed out of the rock. The Centurion got into the boat and Zeno gave him the torch, advising him, at the same time, to be careful to provide himself with another on his return as well as the means of lighting it. He pushed off the shallop, and the impetus was sufficient to bring it to the outlet of the cavern. This was an orifice of small dimensions, and so low that it did not admit of even a sitting posture in the boat. Guiding his skiff therein, Martialis threw his torch into the water and uttered a farewell which rolled in hollow echoes through the cavern. Then he lay down at full length in the boat, and giving a vigorous shove, swept out into the open moonlit sea without. PART III. CHAPTER I.