They fell.
When they came to the surface again, they remained for a few minutes extended on their backs, inhaling the air delightfully.

Arcades, one behind another, opened up amid large walls separating the various basins.

All were filled, and the water stretched in a single sheet throughout the length of the cisterns.

Through the air-holes in the cupolas on the ceiling there fell a pale brightness which spread upon the waves discs, as it were, of light, while the darkness round about thickened towards the walls and threw them back to an indefinite distance.

The slightest sound made a great echo.
Spendius and Matho commenced to swim again, and passing through the opening of the arches, traversed several chambers in succession.