made rough steps here and there, which he knew by heart.  Below, several large fragments of Roman brick and cement lay here and there, where they had fallen in the destruction of the original building.  It was not hard to get down, and the space was not large.  It was bounded by the old wall on one side, and most of the other was taken up by a part of a rectangular mass of masonry, of rough mediaeval construction, which projected inward.

The place was familiar, but Malipieri looked about him carefully, while Masin was climbing down.  Along the base of the straight wall there was a channel about two feet wide, through which the dark water flowed rapidly.  It entered from the right-hand corner, by a low, arched aperture, through which it seemed out of the question that a man could crawl, or even an ordinary boy of twelve.  When they had first come to this place Masin had succeeded in poking in a long stick with a bit of lighted wax taper fastened to it, and both men had seen that the channel ran on as far as it could be seen, with no widening.  At the other end of the chamber it ran out again by a similar conduit.  What had at first surprised Malipieri had been that the water did not enter from the side of the foundations near the Vicolo dei Soldati, but ran out that way.  He had also been astonished at the quantity and speed of the current.  A channel a foot deep and two feet wide carries a large quantity of water if the velocity be great, and Malipieri had made a calculation which had convinced him that if the outflow were suddenly closed, the small space in which he now stood would in a few minutes be full up to within three or four feet of the vault.  He would have given much to know whence the water came and whither it went, and what devilry had made it rise suddenly and drown a man when the excavations had been made under Gregory Sixteenth.

From below, the place where an entrance had then been opened was clearly visible.  The vault had been broken into and had afterwards been rebuilt from above.  The bits of timber which had been used for the frame during the operation were still there, a rotting and mouldy nest for hideous spiders and noisome creatures that haunt the dark.

The air was very cold, and was laden with the indescribable smell of dried slime which belongs to deep wells which have long been almost quite dry.  It was clearly a long time since the little stream had overflowed its channel, but at the first examination he had made Malipieri had understood that in former times the water had risen to within three feet of the vault.  Up to that height there was a thin coating of the dry mud, which peeled off in irregular scales if lightly touched.  The large fragments of masonry that half covered the floor were all coated in the same way with what had once been a film of slime.