After time traveling back thousands of years I've come to discuss Roman aqueducts, which happens to be that giant bridge-like structure in the background.
Aqueducts bring clean water to Roman cities. Otherwise sewage mixes with drinking and bathing water.
Water is pumped from reservoirs and delivered along stone or concrete pipes.
The water then ends up in the fountains of towns and cities or is pumped straight to the villas of wealthy Romans and most importantly, the public baths.
Even without sewage mixing with clean water, it contained parisites such as lice and tapeworms but they couldn't have done much to prevent that.
With the first aqueduct being built in 312 B.C.E., people of the modern world are still amazed by the engineering used to build them, since they had to think about controlling water flow and structure.