THE ANCIENT PEOPLES. 25 
of the pueblos were built on the valley floors or on open 
plains, little thought being given to the ease with which 
the enemy might approach. But because of their 
peculiar arrangement and construction such buildings 
were often easily defended. They were built either 
in the form of a rectangle or a semicircle around a court 
from which they were terraced back toward the outer 
wall which had no openings low enough to be reached 
by the enemy. Some of these, like Aztec on the Animas 
and Pueblo Bonito in Chaco Canyon, had hundreds of 
rooms. <A great number of villages were placed on the 
tops of mesas the walls of which were steep enough to 
furnish a considerable degree of protection. Puyé, 
one of the largest ruins on the Pajarito Plateau, is so 
situated. In many cases a location was chosen just 
above the head of a canyon, on the rim, at each side and 
at the end of which the houses were built, making it 
impossible for the enemy completely to surround the 
settlement. There are ruins in many places which both 
from their character and their location seem to have 
been built solely for defense. These are round or square 
towers of considerable height which have a few small 
openings adapted by their size and location for the 
observation of the enemy and for the discharge of 
arrows. They are usually placed so as to command a 
wide view of the surrounding country, often being 
perched on the top of a boulder or block of stone. 
Materials. The material employed in building ap- 
parently depended upon what was available in the 
particular region. In the San Juan drainage, the sand- 
stone was plentiful and not difficult to work and on the 
Pajarito Plateau there was tufa cut with ease. Asa 
result, in both places there are walls built of well- 
dressed blocks of stone. In other localities the stone is 
in thin strata and was broken off and dressed only 
