as I expected, there was a mass of rubble. I could not doubt
that the whole of the interior of the wall consisted of this
material, and that we should encounter no more blocks of stone
until we came to the outer layer of the wall.

It was easy to understand now why castles deemed impregnable were
sometimes battered down. A thickness of ten feet of stone might
withstand any bombardment, but once the outer stones were pierced,
the lighter material would offer but little resistance to cannon
shot.

That was an afterthought, however; my reflection at the moment was
that liberty was nearer to us by several weeks. Being acquainted
with my discovery, my comrades made no ado when I suggested that we
should now remove another of the stones of the inner wall, so that
we might more easily get at the rubble. Filled with a new spirit of
cheerfulness, they worked with such ardor that in ten nights we
were able to lay a second stone alongside of the first.

But we were now confronted with a new difficulty. It had been easy
enough to dispose of the cement dust: it was quite another thing to
get rid of the vast quantity of small stones and pieces of brick
which now had to be removed. Further, if we cleared all the rubble
from the middle of the wall between us and the outside, there would
be no support for the slabs of the battlement above, and however
firmly they were cemented, it was not improbable that they would
sink in and betray us.

The latter predicament we could but ignore for the present. For the
disposal of the rubble, after some thought I hit upon a plan that
proved entirely successful.

When all was quiet one night, Joe and I descended the ladder which
led from our dormitory to the room below, and lifted, after some
trouble, one of the planks of the floor. As I had hoped, it was not
laid immediately on the ground; a space of two feet deep had been
left. Into this hole night by night we cast the rubble we scooped
out from the wall, carefully replacing the plank when we had done.
We moved always with bare feet, carrying the stuff in our pillow
cases. When I consider how many slight accidents might have marred
our work and utterly undone us, I can not but think that we were in
some sort watched over by Providence. Our life aboard ship had made
us sure footed; but that we were able to work for weeks without
betraying ourselves by a sound or the neglect of some precaution I
ascribe to something higher than ourselves.

T