what it was; "this isn't as easy as it looks. What has
stopped us, Ozma? Is it magic of some sort?"

Ozma was feeling around, her bands outstretched
before her.

"Yes, dear, it is magic," she replied. "The Flatheads
had to have a way from their mountain top from the
plain below, but to prevent enemies from rushing up the
stairs to conquer them, they have built, at a small
distance before the entrance a wall of solid stone, the
stones being held in place by cement, and then they
made the wall invisible."

"I wonder why they did that?" mused Dorothy. "A wall
would keep folks out anyhow, whether it could be seen
or not, so there wasn't any use making it invisible.
Seems to me it would have been better to have left it
solid, for then no one would have seen the entrance
behind it. Now anybody can see the entrance, as we did.
And prob'bly anybody that tries to go up the stairs
gets bumped, as we did."

Ozma made no reply at once. Her face was grave and
thoughtful.

"I think I know the reason for making the wall
invisible," she said after a while. "The Flatheads use
the stairs for coming down and going up. If there was a
solid stone wall to keep them from reaching the plain