Crosswalk, Sidewalk, and Speedbump

Pedestrians can cross without getting feet wet.

Animals pulling carts must walk slowly, straddling the stones.

Gutters and drains keep the street dry.

Aqueducts and Water Supply

Aqueducts bring fresh water to cities.

Water is piped to homes of the wealthy and to public baths.

Fire under the water tank heats bath water.
Exhaust from the fire heats the floor and walls.

Sewers drain waste water away.

The Arch

Acqueducts  and bridges use a series of arches to support the weight of water.

A vault is an aligned row of arches, making a tunnel or ceiling.

The Dome

A dome is a circular array of arches, making a large interior space possible.