To the girls this steel arrangement looked like a triangle, with the base nearest the water.

It came toward them in the form of an arch, stretching out from the palace wall until its end reached the bank and rested there, while the other end still remained on the island.
Then they saw that it was a bridge, consisting of a steel footway just broad enough to walk on, and two slender guide rails, one on either side, which were connected with the footway by steel bars.

The bridge looked rather frail and Dorothy feared it would not bear their weight, but Ozma at once called, "Come on!" and started to walk across, holding fast to the rail on either side.

So Dorothy summoned her courage and followed after.

Before Ozma had taken three steps she halted and so forced Dorothy to halt, for the bridge was again moving and returning to the island.
"We need not walk after all," said Ozma.