middle room or space was built up three stories high, and the walls are
still standing to a height of 28 to 30 feet above the ground level. The
tops of the walls, while rough and greatly eroded, are approximately
level. The exterior surface of the walls is rough, as shown in the
illustrations, but the interior walls of the rooms are finished with a
remarkable degree of smoothness, so much so that it has attracted the
attention of everyone who has visited the ruin. Plate CXV shows this
feature. At the ground level the exterior wall is from 3½ to 4½ feet
thick, and in one place over 5 feet thick. The interior walls are from 3
to 4 feet thick. At the tops the walls are about 2 feet thick. The
building was constructed by crude methods, thoroughly aboriginal in
character, and there is no uniformity in its measurements. The walls,
even in the same room, are not of even thickness; the floor joists were
seldom in a straight line, and measurements made at similar places (for
example, at the two ends of a room) seldom agree.

Casa Grande is often referred to as an adobe structure, but this use of
the term is misleading. Adobe construction consists of the use of molded
brick, dried in the sun, but not baked. The walls here are composed of
huge blocks of rammed earth, 3 to 5 feet long, 2 feet high and 3 to 4
feet thick. These blocks were not molded and then laid in the wall, but
were manufactured in place.

Plate CXVI shows the character of these blocks. The material employed
was admirably suited for the purpose, being when dry almost as hard as
sandstone and nearly as durable. A building with walls of this material
would last indefinitely, provided a few slight repairs were made at the
conclusion of each rainy season. When abandoned, however, sapping at the
ground level would commence and would in time bring down all the walls;
yet in the two centuries which have elapsed since Padre Kino's visit to