When were sewers built to carry waste from the cities?

Sewers designed to carry waste from cities began to be constructed in ancient civilizations, with notable examples from around 2500 BCE in the Indus Valley. The Romans significantly advanced sewer systems around 500 BCE with their Cloaca Maxima, which served as a model for urban sanitation. In the 19th century, the industrial revolution prompted major improvements in sewer infrastructure in cities like London and Paris, driven by public health concerns.