After the fall of the empire, Romans kept throwing filth in the streets, but nobody was washing them. In Rome many sewer pipes fell into disrepair. Everywhere else people got along without them as they always had: at best using latrines (unlined pits) or cesspits (pits lined with perforated masonry that let liquids drain away into the soil while solids piled up for eventual removal) and at worst throwing their waste into the streets and leaving it there. In the 13th century the French king Philip II paved the streets of Paris to reduce the stench, with the result that afterward the waste sat on the stones instead of percolating into the soil. In the 14th century, one of his successors, Philip VI, ordered Parisians to sweep in front of their houses and take the refuse to a dump; crews of sanitation workers were organized to clean up whatever was left. In a return to the technology of the Roman Empire, in 1370 Paris opened a series of drainage canals that also carried waste--the biggest was lined with masonry and called the Grand Egout, or Great Drain. By the 16th century one British royal castle had to post signs reminding people not to "foul the staircases, corridors, or closets with urine or other filth." When the palace of Versailles opened in the 17th century, it had lovely splashing fountains but no bathrooms or sewers.
The world changed in 1842, when the city of Hamburg, after suffering a terrible fire, decided to lay sewer pipes while rebuilding. The new pipes vented through house drains and had a mechanism for flushing using tidewater. The system was efficient, didn't stink, and became a worldwide model. (Before the introduction of these sewers, typhoid, transmitted through water tainted by sewage, caused 48.5 of every 1,000 deaths in Hamburg; after the sewers came into use the number dropped by half.) Immediately thereafter the Parisians began turning their 14th-century sewer system into a wonder of the world, building hundreds of miles of huge brick tunnels to carry away stormwater and everything else Parisians cared to sluice inside.
When early American cities such as Boston and Philadelphia began paving their streets with cobblestones in the 17th century, gutters--and even some underground sewers--were included among the improvements. Private citizens built Boston's first systems, designed, like the Cloaca Maxima and the Grand Egout, to drain cellars and swamps. Bostonians soon grew weary of the constant repairs those wooden sewer lines required and undertook a sort of public-private partnership by issuing construction permits for sewers; everyone who wished to connect a drain had to share in the cost, and the contracts stipulated requirements about pavement reconstruction. Philadelphia had a system of culverts and some underground sewers by 1750, and New York City started putting a few sewers underground later in the century. Human waste, though, remained mostly a personal matter of cesspits and privies.
Sewers really took off in 1854, with John Snow's discovery that the London cholera epidemic was caused by sewage-tainted drinking water. With advances in microbiology, people began to understand that human waste carried disease in the form of microbes, and increasingly they wanted to protect themselves from their sewage. What's more, the introduction of reliable water service in the 19th century and the spread of the modern flush toilet (the British Public Health Act of 1848, which required every home to have some kind of sanitary arrangement, listed "water closet" as one of the alternatives to an ash pit or privy) vastly increased the amount of wastewater households generated. Cesspits and privies that had already created offensive nuisances now produced vast, vile-smelling seepages, overwhelmed by the new volume of water. And it wasn't just toilets, either--connections draining sinks and tubs began overwhelming sewer pipes, too; in 1844 Boston tried to slow the tide, literally, by passing a law requiring a doctor's order for every bath.