To the left was a steep rocky cliff with trees and shrubs growing in the cracks of the rock.

And the canal here left off running along the top of the hill and started to run on a bridge of its own--a great bridge with tall arches that went right across the valley.
Bobbie drew a long breath.
"It IS grand, isn't it ?" she said.

"It's like pictures in the History of Rome." "Right!" said the Doctor, "that's just exactly what it IS like.
The Romans were dead nuts on aqueducts.

It's a splendid piece of engineering." "I thought engineering was making engines." "Ah, there are different sorts of engineering--making road and bridges and tunnels is one kind.

And making fortifications is another.