How does stomach acid help digestion?

Stomach acid is actually hydrochloric acid. Stomach acid is very strong. It can even erode metal if you give it time. Stomach acid breaks down different aspects of food, especially proteins, The body needs broken down particles from food so that it could use it. But, the stomach is not the only thing that breaks down food - the small intestines does too, with bile!

So stomach acid makes food particles smaller so that the body can process it further.

they had the law tat factories that produces smoke cannot be built near residential buildings.

building of proper sewage system was done to ensure that the waste is carried away from the humans so that they do not get diseases from it.

also they built water systems to provide water in those areas which are drought prone.