y thick wall, for the great length of it, as
this was I never have seen in any other place; and so solid was the
building of it that it would have been proof against any ordinary train
of siege artillery. For defence against a foe whose only missile weapons
would be javelins and slings and bows, this great wall made the city
absolutely impregnable. And that the protection that it gave might be
still more complete--and also, as Tizoc explained to us, that in the
case of siege the water supply might be assured, together with a supply
of fish for food--the wall was carried out into the lake so far as to
enclose a basin of more than four acres in extent; within which, should
an enemy gain access to the valley, all the boats upon the lake could be
brought together and held in safety. And finally, the one entrance to
the city was by way of a tunnel-like canal cut in the wall thus rising
from the water; the outer end of which canal was closed in ordinary
times by a heavy grating, while in war time the inner end also could be
closed by means of great metal bars.

It was towards this entrance that the barge that carried us was heading.
Presently we reached it, and the grating was raised for our admission by
means of chains which were operated from the top of the wall. So low and
so narrow was the passage that our heads were within a few inches of the
huge slabs of stone of which its roof was formed; and the rowers had
need to unstep the mast and then to lay their oars inboard, while they
brought the barge through by pushing with their hands against the roof
and sides. The canal was fully forty feet long, and thus the enormous
thickness of the wall was made apparent to us. It truly was, as I
observed to Rayburn, a work that well might be attributed to the
Cyclops.

"I never met a live Cyclop, Professor," Rayburn answered, "and I don't
believe that these fellows ever did either; but it bothers me to know
how they managed to do work like this without a steam-derrick. If we get
out of here with whole skins and our hair on our heads, I hope it won't
be until I've had a chance to talk to some of their engineers, and so
get down to the facts."

A moment later we emerged from the tunnel through the wall, and so
entered the enclosed basin that extended along the whole of the city's
front. Within the basin were lying many canoes, and also boats of a
larger sort that carried oars and that were rigged with a sort of
lug-sail; but these a