The Cloaca Maxima (Greatest Sewer) of Ancient Rome was more than an engineering marvel; it was a watershed moment in the history of public health. Dating back to the 6th century BCE, its design was so cavernous that contemporary accounts claim Roman citizens could navigate sections by boat. In stark contrast, 19th-century London struggled with primitive sanitary conditions that led to 'The Great Stink' long after Rome had mastered the flow of waste. This system did more than prevent flooding—by draining the marshy valleys, it provided the very foundation for the Colosseum and the Roman Forum, proving that 'urban civilization begins beneath our feet.'