hundreds of feet in height, with almost perfectly level surfaces and
precipitous sides. The origin and formation of these _mesas_, due to
erosion through unnumbered centuries, by water draining from an
inland sea, has been already referred to, and it can be readily seen
that they originally formed ideal residences for the peace-loving
Pueblos, who either made their homes as Cliff Dwellers in the
crevices of cañon walls, or took advantage of these lofty rocks,
already shaped and fortified by Nature, and built on them their
dwellings. These in themselves were no mean strongholds. Their thick
walls, made of rock fragments cemented with adobe, constituted a
natural fortress, against which weapons such as savages used before
they acquired fire-arms could do little harm; and even these houses
the Indians constructed like the cliffs themselves, lofty and
perpendicular, tier above tier, and, save for ladders, almost as
inaccessible as eagles' nests. Again, since these _pueblos_ stood on
table-lands, the approach to which could be easily defended, they
were almost impregnable; while their isolation and elevation, in the
treeless regions of New Mexico, enabled watchmen to discover the
approach of an enemy at a considerable distance and to give warning
for the women, children, and cattle roaming on the plain to be
brought to a place of safety. The instinct of self-preservation and
even the methods of defense are, after all, almost identical in every
age and clime; and the motive which led the Indians to the summits of
these _mesas_ was, no doubt, the same that prompted the Athenians to
make a citadel of their Acropolis, and mediaeval knights to build
their castles on the isolated crags of Italy, or on the mountain
peaks along the Rhine.

[Illustration: "CREVICES OF CAÑON WALLS."]