The invention of sewage systems was one of the most important developments in human history, transforming public health and urban life. Before organised sewage systems existed, waste was often thrown into streets, rivers, or open pits, leading to widespread disease and pollution. One of the earliest known sewage systems appeared in the Indus Valley around 2500 BC. Cities like Mohenjo-daro had carefully planned streets with covered drains and even toilets connected to brick-lined sewage channels. This level of hygiene was remarkable for its time and showed a deep understanding of sanitation. The ancient Romans took the idea further. They built an extensive sewer system known as the Cloaca Maxima, which drained wastewater from the city into the River Tiber and served as the backbone of Roman sanitation. In medieval Europe, much of this knowledge was lost. Cities became overcrowded, and waste management declined. Chamber pots were emptied into streets, spreading diseases like cholera and typhoid. In 19th-century London, the problem reached a crisis point. The River Thames, into which raw sewage was discharged, became so polluted that it caused what was known as the "Great Stink" in the summer of 1858. The smell was unbearable, and it overwhelmed the Houses of Parliament, forcing lawmakers to take action. Engineer Joseph Bazalgette was commissioned to design a modern sewer system for the city. His plan involved over 1,100 miles of underground brick sewers that would carry waste away from the densely populated centre of London to treatment areas far downstream. Large pumping stations helped move the sewage through the system. Bazalgette also built embankments along the Thames, which not only housed sewer lines but also reclaimed land for new roads and helped reduce flooding. His attention to detail was extraordinary — he made the sewer pipes far larger than needed at the time, correctly predicting London’s future growth. Completed in the 1860s, Bazalgette's system drastically reduced the spread of waterborne diseases like cholera and laid the foundation for modern urban sanitation. Remarkably, parts of it are still in use today, a lasting legacy of intelligent and forward-thinking design.