to 41/2 feet thick, and in one place at the southern end of the eastern wall, is a trifle over 5 feet thick.  The interior walls are from 3 to 4 feet thick at base.  At the top the walls are reduced to about 2 feet thick, partly by setbacks or steps at the floor levels, partly by exterior batter, the interior wall surface being approximately vertical.  Some writers, noting the inclination of the outer wall surface, and not seeing the interior, have inferred that the walls leaned considerably away from the perpendicular.  This inference has been strengthened, in some cases, by an examination of the interior, for the inner wall surface, while finely finished, is not by any means a plane surface, being generally concave in each room; yet a line drawn from floor level to floor level would be very nearly vertical.  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 on a straight line, and measurements made at similar places, e.g., the two ends of a room, seldom agree.

[Illustration:  Pl.  LV:  West Front of Casa Grande Ruin.]

A series of precise measurements gives the following results:  Outside eastern wall, at level 3 feet above center of depressed area adjoining the ruin on the east, 59 feet; western wall at same level, 59 feet 1 inch; northern and southern walls, at same level, 42 and 43 feet respectively.  These measurements are between points formed by the intersection of the wall lines; the northeastern and southeastern corners having fallen, the actual length of standing wall is less.  At the level stated the northern wall measures but 34 feet 4 inches, and the southern wall 36 feet 10 inches.  A similar irregularity is found in the interior measurements of rooms.  The middle room is marked by an exceptional departure from regularity in shape and dimensions.  Both the east and west walls are bowed eastward, making the western wall convex and the eastern wall concave in reference to the room.

Precise measurements of the middle room at the second floor level, 8 feet above the base previously stated, are as follows:  Eastern side, 24 feet 81/2 inches; western side, 24 feet 2 inches; northern side, 9 feet 31/2 inches; southern side, 9 feet 1 inch.  The eastern room is a little more regular, but there is a difference of 11 inches between the measurements of the northern and southern ends.  A similar difference is found in the western room, amounting there to 6 inches.  The northern and southern rooms do not afford as good bases for comparison, as a corner is missing in each; but measurements to a point where the interior wall surfaces would intersect if prolonged, show variations of from 6 inches to a foot.  The statement that the ruin exhibits exceptional skill in construction on the part of the builders, is not, therefore, supported by facts.